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AGRICULTURAL    ANALYSIS 


PRACTICAL  AGRICULTURAL  CHEMISTRY. 

BY 

J.  BERNARD  COLEMAN,  A.R.C.Sc,  F.I.C. 

AND 

FRANK  T.  ADDYMAN,  B.Sc.Lond.,  F.I.C. 

With  24  Illustrations. 
Crown  8vo.   Is.  6d.  net. 


LONGMANS,  GREEN,  &  CO..  39  Paternoster  Row 
London,  New  York,  and  Bombay. 


AGRICULTURAL   ANALYSIS 


A  MANUAL  OF   QUANTITATIVE   ANALYSIS   FOR 
STUDENTS   OF   AGRICULTURE 


BY 

FRANK   T.  ADDYMAN,  B.Sc.(Lond.),  F.LC. 

n 
CONSULTING   CHEMIST 

LATE   PRINCIPAL  OF  THE  LANCASHIRE  COUNTY  COUNCIL  SCHOOL  OF  AGRICULTURE 

FORMERLY    ASSISTANT    IN    THE    LABORATORY    OF    THE 

ROYAL  AGRICULTURAL  SOCIETY  OF  ENGLAND 


SECOND    EDITION 


LONGMANS,     GREEN,     AND     CO. 

39    PATERNOSTER    ROW,    LONDON 
NEW    YORK    AND    BOMBAY 

1904 
All    rights   reser\ed 


PREFACE 


This  book  is  intended  for  those  students  of  Agri- 
cultural Chemistry  who  desire  a  knowledge  of  com- 
mercial quantitative  analysis. 

The  first  two  chapters  deal  with  ordinary  quanti- 
tative analysis,  and  may  be  omitted  by  those  who 
have  already  received  a  general  training  in  practical 
chemistry.  The  remainder  of  the  book  contains  an 
account  of  those  processes  which  the  experience  of 
qiany  workers  has  shown  to  be  the  most  useful  to 
the  agricultural  analyst. 

In  this  second  edition  the  original  arrangement 
of  the  book  has  been  retained,  but  the  chapters  on 
the  analysis  of  dairy  produce  and  of  water  have  been 
re-written. 

It  would  be  well-nigh  impossible,  in  a  volume  of 
this  size,  to  acknowledge  all  the  sources  to  which  I 
am  indebted  for  assistance,  but  the  mass  of  the  in- 
formation here  given  was  acquired  whilst  working  in 
the  laboratory  of  the  Royal  Agricultural  Society  of 


357291 


vi  Agricultural  Analysis 

England.  For  the  training  received  there,  and  for 
many  courtesies  shown  since  then,  my  most  hearty 
thanks  are  due  to  Dr.  J.  Augustus  Voelcker. 

My  thanks  are  also  due  to  Dr.  Clowes  and  Mr. 
J.  B.  Coleman,  for  permission  to  use  several  wood-cuts 
from  their  manual  of  quantitative  analysis. 

R  T.  A. 
St.  George's  Hospital,  s.w.,  1904. 


CONTENTS 


PART   I 

OPERATIONS   USED  . 

IN  QUANTITATIVE  ANALYSIS 

PAGE 

PAGE 

The  balances    . 

I 

Solution  of  solids    ...       9 

The  weights 

I 

Precipitation 

.  10 

The  rider 

3 

Filtration 

II 

Directions  for  weighing 

3 

Wash  bottles      . 

13 

Desiccators 

4 

The  filter  pump 

14 

Drying  of  solids  . 

5 

Drying  precipitates     . 

15 

The  steam  oven 

6 

Ignition  of  precipitates    . 

16 

The  air  oven 

7 

Burning  the  filter    . 

17 

Evaporation  of  liquids 

8 

I 

>AR^ 

r  II 

THE  MORE   COMMON  ESTIMATIONS  OCCURRING 
IN  AGRICULTURAL   ANALYSIS 


Introductory  remarks 

Section   I.— GRAVIMETRIC  ESTIMATIONS 

Iron  .  .  .  .20 
Sulphuric  acid  .  .  .  .  23 
Potash 24 


Phosphoric  acid 
Calcium 
Carbon  dioxide  . 


20 


26 
28 
31 


Section   II.— VOLUMETRIC  ESTIMATIONS 


Introduction      .         .         . 
Standard  solutions  . 
Indicators .         .         .         . 
Preparation  of  seminormal  sul 
phuric  acid  .         .         , 


37 
38 
39 

40 


Preparation      of     seminormal 

caustic  potash  solution     .     .  42 

Estimation  of  chlorine     .         .  44 

Estimation  of  iron      .         .     .  47 

Estimation  of  sugar         .         .  50 


VUl 


Agricultural  Analysis 


PART  III 
THE  ESTIMATION  OF  NITROGEN 


Introductory  .         . 
Permanent  apparatus .         .     . 
The  soda  lime  process 
The  sulphuric  acid  method .     . 
Estimation  of  N  in  presence  of 
nitrates       .... 


PAGE 

,  56 
56 
58 

.     61 

66 


Nitric,  ammoniacal,  and  organic 

nitrogen  .  .  .  .68 
The  estimation  of  nitric  nitrogen  69 
Ulsch's  method  .  .  .  .  69 
Schloesing's  method  .  .  70 
Lunge's  nitrometer  method      .     80 


PART   IV 

SAMPLES  AND  SAMPLING 

Introductory  . 

82 

Water  samples  .         .         .     . 

88 

Sampling  minerals 

82 

Sampling  of  soils    . 

88 

Sampling  manures  . 

84 

Transit 

89 

Sampling  oil  cakes      . 

87 

Preparation  in  the  laboratory  . 

90 

Sampling  hay,  &c.  . 

87 

PART   V 

THE  ANALYSIS   OF  FEEDING  MATERIALS 


Oil  cakes 
T'eeding  meals 
Grass  and  hay 


92 
102 
104 


Silage 
Roots 


no 
III 


PART   VI 

THE  ANALYSIS  AND    VALUATION  OF  MANURES 


Introductory  remarks     . 

120 

Refuse  manures     . 

145 

Mineral  phosphates  . 

121 

Manure  cakes  . 

.     148 

Basic  slag     . 

130 

Potassic  manures  . 

149 

Bone  meal 

134 

Ammonium  salts 

ISO 

Guano. 

136 

Nitrate  of  soda 

151 

Fish  manure     . 

138 

Compound  manures  . 

151 

Superphosphate  of  lime 

139 

Valuation  of  manures    . 

152 

Dissolved  bones 

144 

Contents 


IX 


PART   VII 

SOIL  ANALYSIS 


Introductory  remarks     . 
Analysis  of  portion  soluble  in 

hydrochloric  acid  .         .     . 
Nitrogen  determination . 
Determination  of  nitrates  and 

chlorides  .  .  .  . 
Determination  of  carbonates  . 
Determination      of      organic 

carbon .         .... 


PAGE 

157 

160 
166 

166 
167 

167 


Analysis  of  insoluble  portion 
Sulphuric  acid  method 
Hydrofluoric  acid  method 
Fusion  method 
Determination  of  '  insoluble 

alkalis 
Analysis  of  limestones 
Analysis  of  lime    . 
Analysis  of  gas  lime . 


PAGE 

168 
168 

169 
169 

171 
173 

176 

176 


PART 

VIII 

THE 

ANALYSIS   OF  DAIRY  PRODUCE 

Milk     . 
Butter      . 

' 

.     178 
.     .     190 

Cheese          .         .         . 

PART 

IX 

WATER  ANALYSIS 

Analysis  of  water  . 

.     200   1 

Remarks       .         .         .         . 

Aependix 

Index     . 

198 


209 

213 
215 


AGRICULTURAL    ANALYSIS 


PART    I 

OPERATIONS   USED  IN    QUANTITATIVE 
ANALYSIS 

The  student  who  has  hitherto  confined  his  attention  to 
general  experiments  and  qualitative  analysis,  will  find  that 
quantitative  work  demands  a  new  kind  of  skill. 

It  is  really  an  art  arising  from  the  Science  of  Chemistry, 
and  just  as  every  other  art  has  its  own  special  technique,  so  the 
art  of  quantitative  analysis  can  only  be  acquired  by  those  who 
have  mastered  certain  simple  operations,  and  have  become 
familiar  with  certain  instruments.  The  chief  of  these  operations 
are  set  out,  and  the  principal  instruments  are  described,  in  the 
following  paragraphs  : 

1.  The  balances  which  are  used  in  different  laboratories 
vary  so  considerably  that  it  is  better  to  leave  all  explanation  of 
their  working  in  the  hands  of  the  teacher. 

2.  The  weights,  however,  are  generally  of  one  description. 
In  the  assay  of  metalliferous  ores  the  grain  is  usually  taken  as 
a  standard  of  weight,  but  for  all  the  purposes  of  the  agricultural 
chemist  the  French  or  metric  system  will  be  found  most 
convenient. 

B 


operations  used,  in  Quantitative  Analysis         [2 


Fig.  I  represents  a  box  of  gram  weights,  which  are  arranged 
in  the  following  order  : 


Brass. 

Platinum. 

Gold  Wire. 

Brass. 

Platinum. 

Gold  Wire. 

IOC 

•5 

•01 

I 

•01 

— 

50 

•2 

•01 

I 

•005 

— 

20 

•I 

•01 

I 

•002 

— 

10 

•I 

•01 

— 

•002 

— 

10 

•05 

•01 

— 

•001 

—     . 

5 

•02 

— 

— 

•001 

— 

2 

•01 

— 

— 

•001 

— 

Of  these,  the  six  smallest  platinum  weights  are  not  as  a 
rule  used,  their  place  being  taken  by  one  of  the  weights  in  the 
third  column.     These  are  known  as  '  riders  '  (paragraph  3). 


Box  of  Weight? 


In  a  laboratory  where  the  balance  is  in  constant  use  it  is  a 
very  convenient  plan  to  keep  the  weights  most  commonly  used 
on  a  piece  of  cardboard,  just  inside  the  balance  case.     The 


3,4] 


Directions  for  Weighing 


cardboard  should  be  marked  off  as  in  fig.  2,  each  square  being 
covered  with  the  weight  whose  value  is  written  upon  it. 

3.  The  rider  is  a  piece  of  wire  bent  so  that  it  may  be 
placed  on  the   graduated  beam  of  the   balance  as  shown  in 


60 

20 

10 

10 

5 

2 

1 

1 

•5 

•2 

•1 

•1 

•05 

•02 

•01 

•01 

Fig.  2.- Card. 


Fig.  3.— Rider. 


fig.  3.  Each  division  of  the  beam  corresponds  to  a  milligram 
(•Qoi).  The  use  of  the  rider,  therefore,  obviates  the  troublesome 
work  of  using  very  small  platinum  weights. 


DIRECTIONS   FOR   WEIGHING 

4.  A  few  minutes'  instruction  from  a  teacher  will  be  found 
more  valuable  than  written  advice.  The  following  rules  will, 
however,  be  of  use  : 

{a)  See  that  the  scale  pans  are  free  from  dust.  If  not, 
cleanse  them  with  a  large  camel's-hair  brush. 

{b)  Always  test  the  balance  before  using  by  releasing  the 
beam  and  allowing  it  to  swing.  The  swings,  as  indicated  by 
the  pointer,  should  be  equal  in  each  direction.  If  the  balance 
be  not  accurate,  it  must  be  adjusted. 

The  two  most  common  attachments  for  effecting  this  adjustment  are  : 

1.  A  small  lever  at  the  centre  of  the  beam,  which  may  be  bent  over 
towards  the  pan  which  is  too  light. 

2.  A  nut  running  on  a  finely  threaded  screw  at  the  end  of  the  beam, 
which  may  be  screwed  towards,  or  away  from,  the  centre  as  required. 

{c)  Place  the  substance  to  be  weighed  on  the  left-hand 
pan,  reserving  the  right-hand  pan  for  the  weights. 

(^  Always  add  the  weights  systematically  in  the  order  in 


4  Operations  used  in  Quantitative  Analysis  [5 

which  they  are  placed  in  the  box  or  on  the  card.  If  the  weight 
on  the  pan  be  too  heavy,  remove  it  and  add  the  next  lighter 
weight.  When  you  have  thus  arrived  at  a  weight  just  too 
light,  leave  it  on  the  pan  and  begin  adding  the  weights 
belonging  to  the  next  decimal  place,  commencing,  as  before, 
with  the  heaviest.  When  all  the  weights  on  the  card  have 
been  tried,  get  the  final  weight  accurately  with  the  rider. 

{e)  Always  raise  the  beam  from  its  bearings  before  adding 
or  removing  a  weight. 

(/)  iNever  weigh  out  a  substance  by  placing  it  directly  on 
the  scale  pan,  but  place  it  in  some  weighed  vessel  of  glass, 
porcelain,  or  platinum. 

{£)  Never  weigh  substances  or  vessels  whilst  they  are 
either  hotter  or  colder  than  the  air  inside  the  balance  case. 

Exercise  I. — Carefully  clean  a  pair  of  watch  glasses  fitted 
with  a  clip,  and  weigh  them.  Powder  some  oxalic  acid.  Place  a 
small  quantity— about  a  gram — in  the  watch  glasses  and  weigh 
again. 

Enter  the  results  in  your  note-book,  thus  : 

Watch  glasses  +  clip  +  H2C2O42H.P 

Watch  glasses  +  clip  = 

H2C20^2H20  = 

Place  the  watch  glasses  with  the  acid  in  a  desiccator  (fig.  4). 

DESICCATORS 

5.  The  desiccator  (fig.  4)  is  an  apparatus  which  is 
intended  to  prevent  hygroscopic  substances  from  gaining 
weight  by  absorption  of  water. 

Substances  which  have  been  heated  are  apt  to  condense 
moisture  on  their  surfaces  when  cooling,  and  thus  to  increase 
in  weight.  To  prevent  this  a  desiccator  is  used.  The  apparatus 
shown  in  fig.  4  is  a  very  convenient  form.  It  consists  of  a 
nearly  air-tight  vessel,  the  air  of  which  is  constantly  kept  dry 


6] 


Desiccators 


S 


by  either  lumps  of  calcium  chloride  or  pieces  of  pumice  saturated 
with  strong  sulphuric  acid.  The  latter  is  objectionable  from  the 
fact  that  in  carrying  the  desiccator  about  the  acid  is  apt  to  be 
splashed  up  on  to  the  substances  above  it.  A  very  convenient 
method  of  charging  the  desiccator  is  to  put  a  couple  of 
handfuls  of  dry  washed  sand 
in  the  bottom  compartment, 
and  pour  just  sufficient  strong 
sulphuric  acid  on  to  the  sand 
to  form  a  firm  mass  which 
will  not  splash  about. 

A  large  desiccator  cap- 
able of  holding  larger  vessels 
is  made  by  placing  a  bell  jar 
on  a  greased  ground-glass 
plate.  Inside  the  chamber 
thus  formed  is  placed  a  glass  dish  containing  some  drying 
agent  and  covered  with  a  piece  of  perforated  zinc. 

If  a  desiccator  be  quite  air-tight,  the  air  which  has  been 
heated  by  the  introduction  of  a  hot  vessel  will  contract  as  it 
cools.  When  such  a  desiccator  is  opened  the  draught  caused 
by  the  inrush  of  air  will  often  displace  light  substances  from 
the  vessel  in  which  they  are  contained,  and  thus  spoil  analyses 
at  the  last  moment.  This  may  be  avoided  by  making  a  deep 
file-mark  on  the  rim  of  the  vessel,  which,  when  the  lid  is 
replaced,  will  leave  a  fine  communication  between  the  outer 
and  inner  air.  This  will  not  render  the  desiccator  any  less 
reliable. 


Fig.  4.—  Desiccator. 


DRYING  OF  SOLIDS 

6.  The  water  contained  in  many  solid  bodies  is  of  two 
kinds,  viz. : — Adherent  water  or  moisture^  and  combined  water 
or  water  of  crystallisation.     Moisture  may  always  be  removed 


6  Operations  used  in  Quantitative  Analysis         [7 

by  heating  for  a  longer  or  shorter  time  at  100°  C,  but  com- 
bined water  often  requires  a  very  much  higher  temperature  for 
its  removal. 

7.  The  apparatus  used  for  keeping  substances  at  a  con- 
stant temperature  of  100°  C,  or  thereabouts,  is  shown  in  fig.  5. 
It  is  known  as  a  steam  oven,  and  consists  of  a  copper  oven  with 
a  double  coating.     The  interval  between  the  two  coatings  is 


Fig.  5. — Steam  Oven. 


partly  filled  with  water.     At  one  side  is  an   arrangement  for 
keeping  the  water  at  a  constant  level  in  the  oven. 

Exercise  II. — Place  the  watch  glass  containing  the  oxalic 
acid  which  has  been  weighed  out  in  Exercise  I.  in  the  steam  oven, 
leaving  the  clamp  in  the  desiccator.  After  it  has  been  heated  for 
two  hours,  replace  the  clamp  and  allow  the  whole  to  cool  in  the 
desiccator ;  then  weigh  it.  Again  remove  the  clamp  and  restore 
to  the  oven  for  half-an-hour,  allow  to  cool  in  the  desiccator,  and 
weigh.  Repeat  this  process  until  two  consecutive  weighings  do 
not  differ  by  more  than  one  milligram.  It  may  now  be  presumed 
that  all  the  moisture  which  can  be  driven  off  at  100°  C.  has  gone. 


8]  Drying  of  Solids  7 

Enter  the  results  under  those  of  the  last  example,  thus  : 

After  dr>ing  i. 
„       ii. 
»         „        iii.       . 
Loss 

The  loss  is  calculated  by  subtracting  the  last  weighing  from  the 
weighing  obtained  in  Example  I. 

Multiply  this  '  loss '  by  100  and  divide  by  the  weight  of  acid 
used  ;  the  quotient  will  give  the  percentage  of  water  which  has 
been  lost. 

8.  For  drying  at  temperatures  between  100°  and  200°  C, 
an  air  oven  is  used.  This  is  very  similar  to  the  steam  oven. 
The  space  between  the  inner  and  outer  coatings  is  occupied  by 
air,  whilst  through  a  hole  in  the  top  is  inserted  a  thermometer 
held  in  position  by  a  perforated  cork. 

Should  it  be  necessary  to  keep  this  bath  at  a  constant  tem- 
perature for  any  length  of  time,  some  form  of  regulator  may  be 
used.  The  one  represented  in  fig.  6 
is  both  simple  and  convenient,  a  is 
a  bulb  about  f  inch  diameter,  blown 
at  the  end  of  a  piece  of  |-inch  glass 
tubing  5  inches  long.  An  inch  from 
the  other  end  is  a  side  tube  (c).  b  is 
a  piece  of  copper  tube  \  inch  dia- 
meter, fitted  into  the  bulb  tube  by  a 
sound  cork.  The  end  of  the  copper 
tube  D  is  slit  up  with  a  fine  saw  for 
about  an  inch.  The  bulb  is  filled 
with  mercury,  and  the  whole  apparatus 
is  fitted  by  a  split  cork  into  the  top  of 
the  air  oven,  b  is  connected  with  the  gas  supply,  and  c  with 
the  burner  which  heats  the  oven.  Should  the  oven  become  too 
hot,  the  mercury  will  rise  and  close  the  slit  d  through  which 


Fig.  6.— Regulator. 


8 


Operations  used  in  Quantitative  Analysis  [9 


the  gas  passes.  Thus  after  a  while  the  temperature  of  the  bath 
becomes  constant.  This  constant  temperature  may  easily  be 
altered  by  sliding  the  tube  b  in  or  out  of  the  bulb  tube.  If 
slid  in,  the  gas  supply  is  decreased,  and  vice  versa. 

Exercise  III.— Weigh  out 
about  I  gram  of  barium  chloride 
as  before,  and  heat  in  the  air 
bath  at  120°  C.  until  of  constant 
weight.  Calculate  the  percent- 
age of  combined  water  as  in 
Exercise  II. 

EVAPORATION   OF 
LIQUIDS 


Fig.  7,— Water  Bath. 


9.  In  quantitative  analysis 
it  is  usual  to  evaporate  liquids 
at  a  temperature  just  below  their  boiling-point.     This  prevents 
loss  by  spirting.     Figs.   7   and  8  show  convenient   forms  of 


Fig.  8. 


water  bath,  though  should  the  bath  be  kept  in  work   con- 
tinuously it   will   be   necessary  to  have  some  attachment   to 


10] 


Evaporation  of  Liquids  g 

Such  an  attachment  is 


keep  the  water  at  a  constant  level, 
shown  in  fig.  5  on  a  steam  oven. 

Either  porcelain,  platinum,  or  nickel  vessels  may  be  used 
for  evaporation,  but  the  most  generally  useful  is  a  beaker  of 
the  form  shown  in  fig.  9.     This  may  be  generally  procured  of 


Fig.  9. 


Fig.  lo. 


very  thin  glass,  which  allows  the  heat  to  pass  freely  from  the 
water  in  the  bath  to  the  liquid  in  the  beaker,  and  moreover 
its  shape  allows  it  to  touch  the  water  (see  fig.  10),  which 
keeps  it  at  a  higher  temperature  than  is  the  case  with  a  vessel 
simply  immersed  in  the  steam. 

Another  method  of  evapora- 
tion will  be  found  in  paragraph 
339,  fig,  49. 

SOLUTION   OF   SOLIDS 

10.  Solution  is  usually  accele- 
rated by  heat,  therefore  sub- 
stances soluble  in  water  should 
be  dissolved  by  heating  with 
water  in  a  beaker  over  a  Bunsen 
flame. 

Should  any  gas  be  evolved 
during  the  process  of  solution — 
e.g.y  when  chalk  or  Iceland  spar  is  dissolved  in  hydrochloric 
acid — precautions  must  be  taken  to  prevent  loss^by  spirting. 
Fig.  1 1  shows  a  very  useful  arrangement. 


Fig.  II. 


lo         operations  used  in  Quantitative  Analysis        [ii 

Exercise  IV.— Weigh  a  clean  watch  glass,  place  upon  it 
about  half  a  gram  of  a  mixture  of  sand  and  chalk,  and  weigh 
again.  Enter  the  results  in  your  note  book.  Place  a  funnel  in 
the  mouth  of  a  conical  flask,  as  shown  in  fig.  ii,  and  wash  the 
powder  off  your  watch  glass  into  the  funnel  with  water  from  a 
wash-bottle  jet.  When  all  the  powder  has  thus  been  transferred 
to  the  flask,  pour  dilute  hydrochloric  acid,  a  little  at  a  time, 
through  the  funnel  into  the  flask  until  effervescence  ceases.  Heat 
the  liquid  to  boiling  in  order  that  all  the  carbonic  acid  may  be 
expelled.  Remove  the  funnel,  and  wash  it,  both  inside  and  out, 
with  the  spray  of  a  wash  bottle,  allowing  the  drops  to  fall  into 
the  flask.  Cover  the  glass  with  a  watch  glass,  and  keep  for 
Exercise  VI. 

PRECIPITATION 

II.  The  student  will  be  perfectly  familiar  with  this  opera 
tion  after  having  studied  qualitative  analysis.  Certain  special 
precautions  must,  however,  be  taken  when  the  contents  of  the 
filter  have  to  be  weighed. 

{a)  The  precipitation  must  be  complete.  This  is  best 
explained  by  taking  an  example.  Suppose  that  it  were  neces- 
sary to  determine  how  much  iron  is  contained  in  a  certain 
solution  of  ferric  chloride.  The  addition  of  ammonia  will 
give  a  precipitate  of  ferric  hydrate ;  but  before  this  precipitate 
is  weighed  it  is  necessary  to  ascertain  whether  sufficient  am- 
monia has  been  added  to  precipitate  the  whole  of  the  iron. 
This  may  be  done  by  allowing  the  precipitate  to  subside  and 
adding  a  little  more  ammonia.  If  no  further  precipitate  be 
formed,  then  the  precipitation  is  complete. 

{!))  Large  excess  of  the  precipitant  is  to  be  avoided. 

{c)  The  precipitate  must  be  obtained  in  a  condition  which 
will  not  readily  pass  through  the  filter  paper.  In  some  cases 
this  takes  place  naturally,  as  in  the  precipitation  of  Fe2(OH)6 ; 
but  in  others  it  causes  considerable  difficulty — e.g.^  barium  sul- 
phate.    In  many  cases  a  good  granular  precipitate  may  be 


12]  Precipitation  ii 

obtained  by  having  both  solution  and  precipitant  at  the  boiling 
point  when  mixing  them. 

{d)  Whenever  hot  water  has  no  solvent  action  on  the  pre- 
cipitate, it  should  be  thrown  down  and  filtered  whilst  the 
solution  is  hot. 

{e)  When  pouring  a  liquid  from  one  vessel  to  another,  pour 
it  down  a  wet  glass  rod  one  of  whose  extremities  touches  the 
side  of  the  vessel  (see  fig.  12). 
This  prevents  loss  by  splashing. 

Exercise  V. — Weigh  out  on  a 
watch  glass  about  -5  gram  of  am- 
monia alum.  Place  this  in  an  8-oz. 
beaker,  and  pour  upon  it  about  50 
c.c.  of  boiling  distilled  water.  Stir 
up  the  liquid  with  a  clean  glass  rod 
until  all  the  solid  has  dissolved. 
Now  pour  dilute  ammonia  carefully 
down  the  side  of  the  vessel  until 
precipitation  is  complete— 2.^.,  until,  ^^^^  ,2. 

after  stirring,  the  liquid  smells  of 

ammonia.  It  is  easy  to  make  a  mistake  in  testing  by  the  smell  of 
ammonia,  as  it  is  quite  possible  that  the  air  in  the  beaker  may 
contain  a  little  ammonia  gas  even  before  the  liquid  has  become 
ammoniacal.  It  is  therefore  necessary  to  blow  the  ammonia 
fumes  away  before  smelling  ;  or  a  piece  of  red  litmus  paper  may 
be  added.  When  this  has  become  blue  the  liquid  contains  excess 
of  ammonia.  Place  the  beaker  over  a  Bunsen  burner  and  heat 
just  to  boiling,  keeping  it  covered  the  while  with  a  clock  glass. 
Place  the  beaker  on  one  side  to  settle. 

FILTRATION   AND   WASHING 

12.  These  operations  are  exactly  like  the  ones  with  which 
the  student  is  familiar.  More  care,  however,  is  required  for 
quantitative  than  for  qualitative  analysis.  The  following  in- 
structions will  show  the  principal  precautions  required  : 

{a)  Special  quantitative  filter  paper  should  be  used#     This 


12         Operations  used  in  Quantitative  Analysis        [12 


paper  is  very  even  in  structure,  and  has  been  washed  free  from 
most  of  its  mineral  matter  by  acids.  A  9-cm.  filter  paper 
when  burned  should  not  leave  a  milligram  of  ash. 

{b)  The  precipitate  should  be  allowed  to  subside,  and  the 
clear  liquid   poured  down  a  glass   rod   into   the   filter   (see 

fig.  13). 

{c)  The  tip  of  the  filter  funnel  should  touch  the  edge  of 
the  beaker  which  is  to  receive  the  filtrate.  This  will  prevent 
splashing. 

{d)  The  precipitate  should  be  washed,  when  possible,  by 
decantation.    When  as  much  of  the  liquid  as  can  be  poured  out 

without  removing  the  sedi- 
ment has  been  transferred  to 
the  filter,  hot  water  is  poured 
on  to  the  precipitate  which  is 
still  in  the  beaker,  and  it  is 
allowed  to  settle.  The  clear 
liquid  is  again  poured  off  as 
before,  and  the  operation  is 
repeated  until  the  filtrate  is 
pure  water.  Finally,  the  pre- 
cipitate is  transferred  to  the 
filter,  the  last  portions  being 
washed  on  to  the  paper  by  the 
wash-bottle  spray.  Should 
any  portions  adhere  to  the  side  of  the  beaker,  they  may  be 
removed  by  rubbing  with  a  glass  rod  tipped  with  a  piece  of 
india-rubber  tubing. 

{e)  Never  use  a  glass  rod  tipped  with  india-rubber  ex- 
cept for  the  operation  above  mentioned.  If  such  a  rod  be 
placed  in  a  liquid  during  precipitation,  some  of  the  pre- 
cipitate may  get  in  between  the  rod  and  the  rubber  and  thus 
be  lost. 


Fig.  13.— Filtration, 


13]  Filtration  and  Washing  13 

(/)  Never  fill  your  filter  with  liquid,  or  some  of  the  pre- 
cipitate may  escape  over  the  edge  of  the  paper. 

{g)  Allow  each  portion  of  washing  liquid  to  drain  away 
before  adding  the  next. 

{h)  Always  evaporate  the  final  washings  to  see  that  no 
further  impurity  is  being  removed  from  the  precipitate. 

A  general  method  of  doing  this  is  as  follows  :  Take  a 
piece  of  thin  glass  (cheap  window  glass  will  do)  and  cut  it  into 
strips  about  three  inches  long  by  half  an  inch  wide.  Thoroughly 
clean  one  of  these  strips,  and  collect  a  few  drops  of  the  filtrate 
on  its  surface.  Next  lay  it  across  the  mouth  of  an  Argand  burner 
which  is  burning  with  a  very  low  flame,  and  allow  the  drop  of 
liquid  to  evaporate.     No  residue  should  be  left  on  the  surface. 

Of  course  this  method  does  not  apply  in  cases  where  the 
precipitate  has  to  be  washed  free  from  acid,  but  this  is  easily 
shown  by  litmus  paper. 

It  should  be  remembered  that  although  a  residue  of  acid 
or  of  ammonium  salts  left  in  a  precipitate  is  entirely  driven  oft 
in  the  subsequent  ignition,  still  much  harm  may  be  done  by 
the  action  of  these  substances  on  the  filter  paper,  making  it 
brittle  and  difficult  to  handle. 

Exercise  VI. — Filter  the  liquid  contained  in  the  flask  after 
Exercise  IV.  through  a  9  cm.  filter,  taking  care  to  observe  all  the 
precautions  above  mentioned,  washing  with  hot  water  by  decanta- 
tion  until  the  filtrate  is  perfectly  free  from  solid  matter.  Keep  the 
precipitate  for  the  following  exercise. 

WASH   BOTTLES 

13.  From  the  student's  work  in  qualitative  analysis  he  will 
be  familiar  with  the  construction  and  use  of  the  ordinary  wash 
bottle.  It  will  be  found  very  convenient  to  keep  two  wash 
bottles  for  quantitative  work,  one  for  cold  and  the  other  for 
hot  water. 


14      Operations  used  in  Quantitative  Analysis      [14,  15 

14.  Occasionally  other  liquids  besides  water  are  necessary 
for  washing  certain  precipitates  ;  for  instance,  ammonium 
phospho-molybdate  must  be  washed  with  dilute  nitric  acid, 
and  ammonium  magnesium  phosphate  must  be  washed  with 
dilute  ammonia.  In  all  cases  where  the  washing  liquid  gives 
off  objectionable  fumes  a  special  form  of  zvash  bottle  is  neces- 
sary. The  stopper  is  drilled  with  three  holes  (see  fig.  14) 
which  contain  respectively  a  short  tube  ter- 
minating both  just  inside  and  just  outside  the 
stopper  (a,  fig.  14),  an  ordinary  tube  with  a 
jet  {b^  fig.  14),  and  a  blowing  tube  with  a  trap 
to  prevent  the  fumes  from  passing  back  into 
the  mouth  (^,  fig.  14).  This  trap  is  very  simple 
in  its  structure,  consisting  merely  of  a  piece  of 
Fig.  14.— Ammonia  india-rubbcr  tubing  stopped  up  at  one  end  by 
^  °"  ^'  a  piece  of  glass  rod,  and  having  a  longitudinal 
slit  about  half-an-inch  long  cut  in  one  side  of  it.  In  using 
this  wash  bottle  the  operator  must  keep  his  finger  on  the  tube 
a  whilst  blowing,  and  remove  it  when  he  wants  the  spray  to 
cease,  otherwise  it  will  continue  to  run  for  some  little  time 
after  the  blowing  has  been  stopped. 


THE   FILTER   PUMP 

15.  In  laboratories  where  a  good  pressure  of  water  is 
obtainable  filtration  may  be  greatly  accelerated  by  the  use  of 
the  filter  pump.  A  very  convenient  form  of  apparatus  is 
shown  in  fig.  15.  a  is  a  Geissler's  filter  pump;  b  is  a  bottle 
with  a  good  cork  doubly  pierced ; .  and  c  is  a  stout  flask 
having  a  tube  sealed  in  one  side  of  its  neck.  By  means  of 
the  pump  a  partial  vacuum  is  caused  in  c,  so  that  the  pressure 
of  the  air  outside  forces  the  liquid  through  the  filter  into  the 


16] 


The  Filter  Pump 


15 


flask.     In  using  the  filter  pump  the  following  precautions  must 
be  taken  : 

{a)  Place  a  small  platinum   cone  at   the   bottom    of  the 
funnel  to  prevent  the  breaking  of  the  filter  paper. 


ib)  See  that  the  paper  fits  exactly  into  the  funnel. 
(c)  Turn  on  the  water  in  the  pump  very  gradually. 
id)  Never  allow  the  filter  to  become  quite  empty. 


DRYING   PRECIPITATES 

16.  The  method  of  drying  depends  on  the  treatment  which 
is  to  follow.  If,  as  is  most  usual,  the  filter  paper  is  to  be 
burned  and  the  precipitate  ignited  and  weighed,  then  the 
drying  may  be  carried  on  rapidly  in  an  air  oven.  A  very  con- 
venient filter  drier  is  easily  made  from  an  old  biscuit  tin.  A 
line  is  drawn  round  the  tin  four  inches  from  the  top.  Sixteen 
holes,  four  on  each  side,  are  made  in  the  tin  along  this  line. 
A  piece  of  No.  16  B.W.G.  copper  wire  is  threaded  backwards 
and  forwards  through  these  holes,  so  as  to  form  a  network 
inside  the  tin,  with  meshes  parallel  to  its  sides.  The  tin  may 
now  be  placed  on  a  large  tripod  in  such  a  manner  that  the 
network  of  wires  is  in  a  horizontal  plane.  The  funnel,  covered 
with  a  piece  of  filter  paper,  is  placed  upright  in  one  of  the 


1 6         Operations  used  in  Quantitative  Analysis   [17,  i8 

meshes,  and  the  cover  placed  loosely  on  the  tin,  which  is  heated 
by  means  of  a  Bunsen  burner. 


IGNITION   OF   PRECIPITATES 

17.  For  this  operation  vessels  made  of  porcelain,  nickel,  and 
platinum  are  used.  Of  these  the  platinum  vessel  is  the  most 
convenient,  but  unfortunately  it  tends  to  form  fusible  alloys 
with  the  heavy  metals.  The  agricultural  analyst,  however,  has 
so   very   seldom   to   ignite   precipitates  which   are  hurtful   to 


Fig.  16. — Argands. 


Fig.  17.— Fletcher. 


platinum  that  he  may  use  vessels  of  that  metal  almost  exclu- 
sively. The  most  useful  form  is  a  capsule  i  inch  deep  by 
2  inches  diameter,  as  shown  in  fig.  16. 

18.  When  a  platinum  vessel  is  frequently  heated  over  a 
Bunsen  flame  it  tends  to  blister,  and  a  grey  deposit  forms 
where  the  flame  has  touched  it.  After  a  little  while  it  begins 
to  lose  weight,  and  in  time  the  capsule  becomes  worn  out. 

This  may  be  avoided  in  a  great  measure  by  cleaning  the 
vessel  frequently  with  sea-sand,  whose  rounded  granules 
smooth  down  the  minute  blisters  which  give  the  grey  ap- 
pearance. 


19,  20]  Ignition  of  Precipitates  1 7 

19.  A  better  plan  is  never  to  let  a  flame  touch  the  platinum. 
Whenever  a  precipitate  is  to  be  ignited,  an  Argand  burner 
should  be  used  of  one  of  the  forms  shown  in  fig.  16. 

The  support  for  the  capsule  is  made  either  of  platinum 
wire,  or  of  iron  wire  round  which  has  been  fastened  a  strip 
of  platinum  foil.  Should  a  higher  temperature  be  required, 
as  in  the  burning  of  CaC03  to  CaO,  a  Fletcher  muffle  furnace 
may  be  used  (see  fig.  17). 


BURNING   TPIE   FILTER 

20.  This  operation  is  carried  out  in  several  ways,  but  for 
the  purposes  of  this  book  only  two  need  be  described. 

{a)  When  the  burning  of  the  filter  has  no  action  on  the 
precipitate,  the  filter  paper  may  be  folded  up  whilst  still  wet, 
placed  in  a  platinum  dish,  and  ignited  very  gradually  over  an 
Argand. 

{b)  In  other  cases  the  precipitate,  dried  as  described  in 
paragraph  16,  is  removed  as  completely  as  possible  from  the 
filter  paper  to  the  dish,  and  the  paper  burned  in  a  coil  of 
platinum  wire. 

If  the  wire  be  wound  carelessly  about  the  paper,  it  will 
probably  break  after  being  used  a  few  times,  from  being  con- 
tinually bent  about  in  different  ways.  This  is 
avoided  by  winding  the  wire  in  a  spiral  around 
a  small  cone  of  wood.  When  required  for  use 
the  wooden  cone  is  removed  and  the  filter  folded 
up  and  introduced  into  the  spiral  as  in  fig.  18. 

The  operation  of  burning  is  shown  in  fig.  19.  The  spiral 
of  wire  containing  the  filter  is  held  over  the  platinum  dish, 
which  stands  on  a  glazed  tile.  Should  the  precipitate  be  dark 
coloured,  a  white  tile  is  used ;  should  it  be  light,  a  red  one  is  to 
be  preferred.     First  the  paper  is  ignited  by  the  Bunsen  burner, 

c 


Fig.  18. 


1 8         Operations  used  in  Quantitative  Analysis 


[20 


and  allowed  to  burn  quietly  until  the  last  spark  dies  out.  Then 
the  burner  is  used  to  keep  it  red  hot  until  all  the  carbonaceous 
matter  is  burned  off.     The  ash  is  then  shaken  out  into  the 


Fig. 


dish,  and  the  last  traces  removed  from  the  wire  with  a  small 
cameFs-hair  brush.  Finally,  any  portions  of  the  ash  which  may 
have  fallen  on  the  tile  are  swept  into  the  dish.  The  dish  is 
then  ready  for  ignition  and  weighing. 

Exercise  VII. — Carefully  clean  a  platinum  dish  of  the  size  de- 
scribed in  paragraph  17.  Place  it  over  an  Argand,  as  in  fig.  16, 
until  red  hot.  Remove  it  to  a  desiccator,  and  when  quite  cool 
weigh  it.  Place  the  wet  filter  paper  containing  the  sand  which  has 
been  washed  in  performing  Exercise  VI.  in  this  dish,  and  heat 
over  an  Argand  turned  down  until  the  flame  is  as  small  as  possible. 
Whilst  it  is  drying  start  Exercise  VIII.  When  steam  ceases  to 
come  off,  turn  up  the  burner  until  the  dish  becomes  red  hot.  The 
paper  will  catch  fire  and  burn.  When  nothing  is  left  but  the  sand 
and  the  white  ash  of  the  filter  paper,  remove  to  a  desiccator,  and 
when  cool  weigh.     Enter  your  results  thus  : 

Dish  +  sand  +  ash  = 

Dish  =      

Sand  +  ash  = 

Filter  ash  = 

Sand  = 

From  this  calculate  what  percentage  of  sand  was  contained  in  the 
mixture  dissolved  in  Exercise  IV. 


20]  Burning  the  Filter  19 

Exercise  VIII. — Whilst  the  ignition  described  above  is  going 
on,  filter  off  the  alumina  precipitate  obtained  in  Exercise  V.,  wash- 
ing it  thoroughly  by  decantation.  Dry  in  the  arrangement  de- 
scribed in  paragraph  16,  and  burn  it  as  described  in  paragraph  20^, 
first  weighing  the  dish  as  in  Exercise  VI  I.  Finally,  ignite  the 
dish  and  precipitate,  cool  in  a  desiccator,  and  weigh.  Enter  the 
results  just  under  the  entry  for  Exercise  V.,  and  calculate  the 
percentage  of  Al^Og  which  you  have  precipitated  out  of  the 
ammonia  alum. 


PART    II 

THE  MORE   COMMON  ESTIMATIONS 
OCCURRING  IN  AGRICUITURAL  ANALYSIS 

21.  No  one  can  expect  to  attain  proficiency  in  any 
branch  of  quantitative  analysis  unless  he  first  acquire  confi- 
dence in  the  accuracy  of  his  work.  The  most  simple  way  of 
acquiring  confidence  is  to  practise  the  different  estimations  on 
pure  substances  of  known  composition.  The  results  are  in 
this  way  easily  checked.  By  working  systematically  through 
this  section,  using  always  the  substance  recommended,  the 
student  will  gain  the  necessary  confidence  and  at  the  same  time 
acquire  a  knowledge  of  all  the  simpler  operations  used  in 
agricultural  analysis. 

Always  read  thf'ough  the  whole  oj  a  paragraph  before  covi- 
menctng  the  work  described  therein. 


Section  I.-GRAVIMETRIC  ESTIMATIONS 

ESTIMATION   OF   IRON 

2  2.  Substance  used. — Ferrous  ammonium  sulphate, 
Fe(NH4)2(S04)2.6H20. 

Method  employed. — The  iron  is  precipitated  as  ferric 
hydrate  and  weighed  as  ferric  oxide,  Fe203. 

Weigh  out  in  a  watch  glass  about  *5  gram  of  pure  ferrous 
ammonium  sulphate  which  has  been  finely  powdered  and 
pressed  between  folds  of  filter  paper.  Transfer  this  to  a  lo-oz. 
beaker,  washing  the  last  traces  of  substance  from  the  watch 
glass  by  means   of  the   wash  bottle,  and   dissolve   in  about 


23-25]  Estimation  of  Iron  21 

30  c.c.  of  hot  water,  using  a  few  drops  of  dilute  H2SO4  to  clear 
the  solution.  The  water  must  be  poured  down  the  sides  of 
the  beaker  to  avoid  all  risk  of  splashing. 

23.  Precipitation. — Raise  the  liquid  to  boiling-point 
over  a  Bunsen  burner,  and  add  gradually  5  c.c.  of  strong  nitric 
acid.  The  liquid,  which  has  hitherto  been  only  just  coloured, 
will  now  acquire  a  deep-yellow  tint  from  the  oxidation  of  the 
ferrous  to  a  ferric  salt.  After  it  has  boiled  for  a  few  seconds 
remove  it  from  the  burner,  and  add  dilute  ammonia  (3  of 
distilled  water  to  i  of  strong  ammonia)  cautiously.  Stir  with 
a  glass  rod.  Place  a  very  small  piece  of  litmus  paper  in  the 
beaker.  Continue  adding  ammonia  until  the  litmus  paper 
shows  a  distinctly  alkaline  reaction.  A  flocculent  precipitate 
of  ferric  hydrate  will  be  thrown  down.  Cover  the  beaker  with 
a  clock  glass,  replace  it  over  a  Bunsen  flame,  and  allow  it 
to  boil  for  about  a  minute.  Turn  out  the  light,  and  allow  the 
precipitate  to  settle. 

It  is  very  convenient  to  have  a  small  wash  bottle  of  about 
8  oz.  capacity  containing  ammonia,  the  jet  of  liquid  being 
much  preferable  to  the  unmanageable  stream  which  comes  from 
the  mouth  of  a  bottle.  The  special  form  of  wash  bottle  de- 
scribed in  paragraph  14  is,  however,  necessary.  The  ordinary 
form  would  often  fill  the  operator's  mouth  with  ammonia  fumes. 

24.  Filtration  and  Washing. — Whilst  the  precipitate  is 
settling,  fit  a  9-cm.  filter  paper  into  a  clean  glass  funnel,  and 
moisten  it  with  hot  water.  When  the  precipitate  has  settled 
smear  the  outside  of  the  lip  of  the  beaker  with  the  smallest 
possible  quantity  of  lard  or  vaseline,  and  pour  the  clear  liquid 
down  a  clean  glass  rod  into  the  filter  paper.  Wash  the  pre- 
cipitate by  decantation  exactly  as  directed  in  paragraph  12  (d). 

25.  Drying,  Igniting,  and  Weighing.— Cover  the 
top  of  the  funnel  with  a  piece  of  filter  paper,  and  dry  it  in  the 
oven  described  in  paragraph  16.     Whilst  it  is  drying  clean  a 


22    Estimations  occurring  in  Agricultural  Analysis   [26 

platinum  dish  2  inches  in  diameter  by  i  inch  in  depth.  Heat 
it  to  redness  over  an  Argand.  Allow  it  to  cool  in  a  desiccator 
and  weigh  it.  Enter  the  result  as  shown  below.  Place  the 
dish  on  a  clean  white  glazed  tile,  and  transfer  into  it  as  much 
as  possible  of  the  dried  precipitate.  Burn  the  filter  paper  in 
a  spiral  of  platinum  wire  exactly  as  directed  in  paragraph  20. 
Shake  the  ash  into  the  dish.  With  a  small  camel's-hair  brush 
sweep  into  the  dish  every  particle  which  has  drifted  over  on  to 
the  tile.  Place  the  dish  with  its  contents  over  an  Argand,  and 
ignite  at  a  red  heat  for  two  or  three  minutes,  or  until  any  scrap 
of  charred  filter  which  has  escaped  burning  in  the  wire  is  com- 
pletely reduced  to  ash.  Allow  to  cool  in  a  desiccator,  and  weigh. 
26.  Entry  and  Calculation. — The  following  example 
shows  the  method  of  entry  in  the  laboratory  note  book.  The 
weights  are  entered  on  the  right-hand  page,  and  the  calcula- 
tions made  on  the  left : 


2Fe  +  30  =  F'ePj. 

Glass +Fe(NlIJ,(S0J,6Hp' 

112  +  48  =160. 

=  6-0832 

.-.  160  FePa  contains  112  Fe 

Glass 

=  5-6194 

I       „         „           112 

Fe(NH,),(S0,),6H,0 

=     -4638 

160 

7 

Dish +  Fe.,03  + Ash 

=  16-1741 

.^«.T                                                                                -0941X1^2 

Dish 

=  16-0798 

•0941                „                      „                                                ^ 

Fe.,03  +  Ash 

=  ^^946 

10 

Ash 

=     -0005 

•0941 

7 
•06587  =  Fe 

Fe,03 

=     -0941 

4638 )  6587  (  14-20  %Fe 

4638 

19490 

18552 

9380 

9276 

104 

Percentage  of  Fe  found         =14-20 

,,             calculated  =  14-29 

27-29]  Estimation  of  Sulphuric  Acid  23 

ESTIMATION   OF  SULPHURIC   ACID   (SO3) 

27.  Substance  used.— Copper  sulphate,  CUSO4.5H2O. 
Method  employed.— The  SO3  is  precipitated  by  barium 

chloride  and  weighed  as  barium  sulphate. 

Weigh  out  about  '5  gram  of  pure  crystallised  copper  sul- 
phate on  a  watch  glass.  Transfer  to  a  lo-oz.  beaker,  and 
dissolve  as  in  the  previous  estimation,  using  HCl  instead  of 
H2SO4  to  clear  the  solution. 

28.  Precipitation. — Add  to  the  liquid  in  the  beaker 
about  20  c.c.  of  ammonium  chloride  solution  and  bring  it  to 
the  boil  over  a  Bunsen.  The  reason  for  adding  this  NH4CI  is 
that  barium  sulphate  is  thrown  down  in  a  more  granular  form 
in  the  presence  of  this  salt  than  is  otherwise  the  case.  This 
minimises  the  risk  of  the  precipitate  being  so  fine  as  to  pass 
through  the  pores  of  the  filter  paper,  which  is  the  chief 
difficulty  with  this  estimation.  As  soon  as  the  solution  boils 
add  excess  of  boiling  barium  chloride  solution.^  Cover  the 
beaker  with  a  watch  glass,  and  boil  for  about  half-a-minute ; 
then  allow  the  precipitate  to  settle  completely.  Add  another 
drop  of  barium  chloride  to  make  sure  that  no  sulphate  re- 
mains in  solution.  Should  a  further  precipitate  be  caused,  the 
liquid  must  be  stirred,  reheated,  and  a  further  quantity  of 
boiling  barium  chloride  added. 

If  the  above  directions  have  been  followed  exactly,  the 
barium  sulphate  will  have  settled  in  about  ten  minutes. 

29.  Washing. — The  precipitate  should  be  washed  about 

five  times  by  decantation  (paragraph  12),  then  transferred  to 

the  filter  and  washed   with   hot   water  from  the  wash   bottle 

until  a  few  drops  of  the  filtrate  no  longer  give  a  cloudiness 

when  tested  with  sulphuric  acid.     The  test  tube  in  which  this 

'  For  the  estimation  of  sulphuric  acid  the  ordinary  barium  chloride 
solution  is  not  very  satisfactory :  a  saturated  solution  should  be  used. 


24  Estimations  occurring  in  Agricultural  Analysis  [30-33 

test  is  performed  should  be  allowed  to  stand  for  about  a 
minute,  as  it  often  takes  that  time  before  the  cloudiness 
appears. 

30.  Burning  and  Ignition. — The  precipitate  is  dried 
(paragraph  16)  and  transferred  to  a  platinum  dish,  as  in  the  esti- 
mation of  iron.  Great  care  must,  however,  be  taken  thoroughly 
to  burn  the  filter  paper  on  the  wire.  Any  carbonaceous 
matter  dropped  into  the  dish  tends  to  reduce  a  portion  of  the 
BaS04  to  BaS.  This,  however,  will  not  take  place  in  a  good 
current  of  air  such  as  is  kept  up  around  the  hot  wire.  Further, 
it  should  be  mentioned  that  a  shallow  dish  is  preferable  to  a 
deep  crucible  for  the  ignition.  A  shallow  dish  will  afford  every 
opportunity  for  the  free  circulation  of  the  air;  a  deep  crucible 
will  keep  out  the  air.  With  these  special  precautions,  the 
burning  of  the  filter  and  subsequent  ignition  over  an  Argand 
may  be  performed  as  described  in  paragraphs  20  and  18. 

31.  Entry  and  Calculation. — The  results  should  be 
entered  in  the  note  book  as  shown  in  paragraph  26,  and  the 
calculation  made  in  much  the  same  way.  One  molecule  of 
BaS04  corresponds  to  one  of  SO3 ;  or  233  parts  by  weight  of 
BaS04  correspond  to  80  parts  by  weight  of  SO3. 

ESTIMATION   OF   POTASH 

32.  Substance  used.— Potassic  chloride,  KCl. 
Method  employed. — The   potassium  is  precipitated  as 

KgPtClG,  and  weighed  as  such. 

Weigh  out  about  '3  gram  of  pure  potassic  chloride,  and 
wash  it  off  the  watch  glass  into  a  wide-mouthed  beaker 
2  inches  high  by  2  inches  broad,  using  as  little  water  as  pos- 
sible. Add  sufficient  water  to  dissolve  it,  then  two  or  three 
drops  of  dilute  hydrochloric  acid. 

33.  Precipitation, — Pour  into  the  liquid  6  c.c.  of  a  10  per 


34,  35]  Estimation  of  Potash  25 

cent,  solution  of  platinum  chloride,  and  evaporate  on  the 
water  bath.  Evaporation  must  be  continued  until,  on  removing 
the  beaker  from  the  water  bath,  the  liquid  sets  to  a  pasty  con- 
dition. If  it  has  evaporated  to  dryness  a  few  drops  of  water 
should  be  added,  and  evaporation  continued  until  the  pasty 
condition  is  reached.  The  beaker  is  then  allowed  to  cool, 
and  strong  alcohol  is  added  and  gently  swilled  around  the 
beaker  until  the  liquid  is  of  uniform  colour. 

34.  Filtration  and  Washing.  —  Two  pieces  of  filter 
paper  are  taken  and  placed  one  in  each  pan  of  the  balance, 
and  the  heavier  one  trimmed  with  a  sharp  pair  of  scissors  until 
the  two  are  identical  in  weight.  They  are  then  folded  together 
and  placed  in  a  funnel.  The  alcoholic  liquor  is  poured  through 
them,  and  the  crystalline  precipitate  washed  with  alcohol  by 
decantation  until  the  filtrate  is  colourless.  The  precipitate  is 
then  transferred  to  the  filter,  and  washed  with  alcohol  until  the 
filter  papers  appear  quite  white  and  the  filtrate  is  no  longer 
yellow.  In  this  operation  the  flaky  crystals  of  the  precipitate 
should  not  be  broken  up.  Further,  the  india-rubber  tip  to  the 
glass  rod  must  not  be  used,  as  the  alcohol  is  apt  to  render  it 
sticky.  The  filter  papers  are  dried  in  the  steam  oven,  cooled 
in  a  desiccator,  and  separated.  The  blank  filter  is  put  on  the 
pan  with  the  weights,  and  the  one  containing  the  KgPtClg  on 
the  other,  and  the  difference  is  weighed. 

By  this  method  the  two  filters  are  both  treated  in  the  same 
way,  and  will  therefore  lose  weight  equally.  The  error  which 
would  creep  in  if  the  filter  paper  were  simply  weighed  and  its 
weight  subtracted  from  the  total  weight  of  paper  and  KgPtCle 
is  thus  eliminated. 

35.  Another  method  of  arriving  at  the  weight  of  the  pre- 
cipitate— which,  however,  takes  a  slightly  longer  time — is  as 
follows  : 

Filter  off,  and  wash  on  an  ordinary  filter  paper.     Dry  at  100°, 


26  Estimations  occurring  in  Agricultural  Analysis  [36.  37 

then  transfer  as  much  as  possible  of  the  precipitate  to  a  weighed 
platinum  dish.  Replace  the  filter  in  the  funnel,  and  wash  it 
two  or  three  times  with  small  quantities  of  boiling  distilled 
water,  allowing  the  washings  to  run  into  the  platinum  dish. 
When  the  adhering  precipitate  has  entirely  disappeared  from 
the  filter,  place  the  dish  on  the  water  bath  until  the  water  has 
evaporated.  Remove  it  to  the  steam  oven  for  a  few  minutes. 
Cool  in  a  desiccator,  and  weigh. 

36.  Calculation. — From  the  weight  of  KsPtClg  the  weight 
of  K  may  be  obtained,  or,  as  is  more  usual  in  agricultural 
chemistry,  an  equivalent  quantity  of  K2O  may  be  calculated. 
(See  paragraph  251.) 

When  a  large  number  of  analyses  have  to  be  made  in  a 
given  time,  it  is  of  importance  to  make  the  calculation  as  short 
as  possible.  To  this  end  '  factors '  are  usually  employed'. 
The  factor  for  calculating  how  much  KgO  is  represented  by 
a  given  quantity  of  KgPtClgis  -19308,  or,  as  is  more  frequently 
used,  •193.  Thus  in  calculating  out  the  result  of  this  estima- 
tion we  use  the  following  formula  : 

Wt.  of  K^PtClg  X  100  _ 

Wt.  of  substance  taken  X  '^93  -  /o  ot  )^^KJ. 


ESTIMATION   OF   PHOSPHORIC   ACID   (P2O5)  ^ 

37.  Substance  used.— Sodium  hydrogen  phosphate, 
Na:HPO,.i2H20. 

Method  employed.— The  phosphoric  acid  is  precipi- 
tated as  Mg.NH4.PO4.6H.2O,  which  is  ignited  and  weighed  as 
Mg^PoO^. 

'  When  phosphatic  manures  are  guaranteed  to  contain  a  certain  per- 
centage of  phosphoric  acid,  V.f)„  is  usually  meant.  The  one  exception  to 
this  rule  is  liquid  phosphoric  acid,  which  is  generally  guaranteed  to  con- 
tain a  percentage  of  HaPO^. 


38,  39]  Estimation  of  Phosphoric  Acid  27 

Before  starting  this  analysis,  a  stock  of  magnesia  mixture 
should  be  prepared  as  follows  : 

Preparation  of  magnesia  mixture. — Dissolve  60  grams 
MgCl2  and  80  grams  NH4CI  in  600  c.c.  of  distilled  water. 
Add  400  c.c.  strong  ammonia  (Sp.G.  =  "880),  and  allow  to 
stand  twenty-four  hours.     Filter  off  any  sediment. 

MgS04  is  sometimes  used  instead  of  MgCl2,  but  is  objec- 
tionable, as  a  basic  sulphate  of  magnesia  is  often  precipitated 
with  the  magnesium  ammonium  phosphate. 

Weigh  out  about  i  gram  of  pure  Na2HP04.i2H20. 
Transfer  to  a  12-oz.  beaker,  and  dissolve  in  about  100  c.c. 
of  distilled  water. 

38.  Precipitation. — Measure  off  30  c.c.  of  the  magnesia 
mixture  and  pour  it  into  the  beaker.  Stir  well  for  a  few 
seconds.  Add  20  c.c.  strong  ammonia  and  stir  again.  Now 
cover  the  beaker  with  a  clock  glass  and  allow  it  to  stand  in  a 
cool  place  for  2\  hours,  stirring  it  once  every  fifteen  minutes. 
At  the  end  of  this  time  precipitation  will  be  complete.  Should 
it  be  found  more  convenient  to  allow  the  beaker  to  stand  over- 
night, it  will  be  advisable  to  add  10  c.c.  strong  ammonia  next 
morning  and  stir  well.  When  the  precipitate  has  subsided  it 
will  be  ready  for  filtering. 

39.  Filtration  and  Washing.— The  precipitate  in  this 
case  must  not  be  washed  by  decantation,  but  must  be  got  on 
to  the  filter  paper  at  once.  It  is  much  quicker,  however,  to 
decant  the  clear  liquid  through  the  filter  than  to  filter  the  turbid 
liquid.  When  all  the  clear  portion  has  passed  through,  wash 
the  pasty  precipitate  on  to  the  filter  with  dilute  ammonia  (i  of 
•880  NH3  to  3  of  H2O),  using  the  special  form  of  wash 
bottle  described  in  paragraph  14.  Wash  the  precipitate  six 
times  with  ammonia,  allowing  each  portion  to  run  through 
before  adding  the  next.  Test  a  few  drops  of  the  filtrate  with 
excess  of  dilute  HNO3  and  a  drop  of  AgNO^.     No  cloudiness 


28  Estimations  occurring  in  Agricultural  Analysis  [40-42 

should  appear.     If  this  test  shows  that  the  precipitate  is  not  yet 
free  from  chlorides,  it  should  receive  further  washing, 

40.  Ignition  and  Weighing.— After  the  filter  has  been 
dried  (paragraph  16),  transfer  as  much  as  possible  to  a  platinum 
dish.  Burn  the  filter  paper  completely  in  the  platinum  spiral 
(see  fig.  19).  Place  the  ash  in  the  dish,  and  remove  it  to  an 
Argand  which  is  turned  down  to  the  smallest  possible  flame. 
The  flame  is  increased  gradually  until,  in  about  forty  minutes, 
the  dish  is  at  a  dull  red  heat.  Now  watch  it  until  a  bright  red 
glow  passes  suddenly  over  the  precipitate  and  dies  away  again. 
Turn  up  the  Argand  until  the  dish  is  as  hot  as  possible,  and 
ignite  for  about  five  minutes.     Cool  in  the  desiccator  and  weigh. 

41.  Calculation. — One  molecule  of  MgaPoO;  corresponds 
to  one  of  P2O5,  hence  the  quantity  of  P2O5  in  the  quantity  of 
Na2HPO,.i2H20  taken  may  be  calculated,  and  from  this  the 
percentage.  The  factor  for  converting  Mg2P207  into  P2O5  is 
•64,     Thus : 

Wt.  of  Mg2P207  X  100       ^    _  0/    f  p  n 
Wt.  of  Na2HP04.i2H20  ^  "^^  -  />  of  1  ..O,. 

N.B.  If  this  exercise  has  been  carefully  worked,  the  percentage  of 
P2O5  found  will  be  lower  than  that  required  by  theory,  as  the  magnesium 
ammonium  salt  is  slightly  soluble  in  dilute  ammonia.  For  further  dis- 
cussion of  this  error  see  paragraph  200. 


ESTIMATION   OF  CALCIUM 

42.  Substance  used.— Calcium  carbonate,  CaCO^. 

Method  employed. — The  calcium  is  precipitated  as 
calcium  oxalate,  and  either  heated  gently  and  weighed  as 
CaCOa,  or  ignited  strongly  and  weighed  as  CaO. 

Weigh  out  about  '5  gram  powdered  Iceland  spar,  wash  into 
a  1 2-oz.  beaker,  and  cover  with  a  clock  glass.     Insert  the  jet  of  a 


43,  44]  Estimation  of  Calcium  29 

wash  bottle  containing  dilute  HCl  between  the  clock  glass  and 
the  edge  of  the  beaker,  and  blow  the  acid  so  that  the  spray  may 
strike  the  opposite  side  of  the  vessel  and  descend  gently  upon  the 
spar.  When  about  50  c.c.  have  been  added,  allow  the  beaker 
to  stand  in  a  warm  place  (on  the  top  of  the  steam  oven  will  be 
found  very  convenient)  until  all  effervescence  ceases.  Should 
any  of  the  substance  remain  undissolved,  add  a  little  more 
acid.  Remove  the  clock  glass,  and  wash  any  liquid  adhering 
to  it  back  into  the  beaker. 

43.  Precipitation. — The  precipitate  obtained  when  a 
solution  containing  calcium  is  mixed  with  one  containing  an 
oxalate  is  of  such  fine  texture  that  it  often  passes  through  a 
filter  paper  and  thus  causes  much  annoyance.  This  difficulty 
may  be  overcome  in  the  following  manner  : 

Dilute  the  solution  to  about  150  c.c. ;  make  alkaline  with 
dilute  NH3,  and  heat  until  it  just  boils.  Whilst  it  is  heating 
weigh  out  roughly  a  gram  of  pure  finely  powdered  ammonium 
oxalate.  Remove  the  beaker  from  the  flame  and  add  the  solid 
ammonium  oxalate  a  little  at  a  time,  stirring  continuously. 
Replace  the  beaker  over  the  flame  and  raise  to  a  boil ;  then 
stop  heating,  and  allow  the  precipitate  to  settle.  This  will  not 
take  more  than  a  minute  or  two. 

In  using  this  method  care  must  be  taken  to  remove  the 
beaker  from  the  influence  of  the  flame  before  adding  the 
oxalate  to  the  solution.  If  this  be  not  attended  to,  an  effer- 
vescence will  take  place  which  may  cause  the  loss  of  some  of 
the  solution. 

The  oxalate  should  be  tested  by  placing  about  2  grams  in 
a  weighed  platinum  crucible  and  heating  to  redness.  The  salt 
should  volatihse  entirely,  leaving  no  residue — i.e.^  the  crucible 
should  not  gain  in  weight. 

44.  Washing  and  Filtration.— Wash  about  six  times 
by  decantation,  then  once  or  twice  on  the  filter,  testing  the 


30  Estimations  occurring  in  Agricultural  Analysis  [45,  46 

final  washings  by  means  of  a  glass  slip,  as  described  in  para- 
graph 12  {1i). 

45-  Ignition  and  Weighing. — Dry  the  precipitate,  and 
prepare  it  for  weighing  as  follows :  Remove  as  much  of  the 
precipitate  as  possible  from  the  paper  to  a  weighed  platinum 
dish,  keeping  it  well  on  one  side  of  the  dish.  Burn  the  filter 
rapidly  on  a  spiral  of  platinum  wire,  and  whilst  still  black  drop 
it  into  the  dish,  so  that  it  may  lie  in  direct  contact  with  the 
platinum  and  not  on  top  of  the  calcium  oxalate.  Place  the 
dish  on  an  Argand  with  the  flame  turned  low,  and  gradually 
turn  it  up  until,  in  about  half-an-hour,  it  is  just  below  a  red 
heat.  Now  watch  the  filter  paper  carefully  for  a  few  minutes. 
If  it  should  begin  to  burn,  or  if  sparks  appear  on  its  surface, 
the  flame  must  be  lowered.  If  in  the  course  of  half-an-hour 
the  paper  is  still  perfectly  black,  the  flame  must  be  turned  up ' 
a  little.  When  the  right  temperature  is  obtained  in  this  way 
the  paper  will  gradually  crumble  down  to  a  light-grey  coloured 
mass.  As  soon  as  all  the  black  of  the  filter  has  gone,  which 
should  take  place  in  about  forty  minutes  from  commencing, 
the  dish  may  be  cooled  down  in  a  desiccator  and  weighed. 

A  very  little  practice  is  sufficient  to  enable  the  analyst  to 
hit  the  right  temperature  for  this  reaction,  but  a  second  weigh- 
ing is  generally  advisable  after  heating  at  the  same  temperature 
as  before  for  ten  minutes  longer.  The  second  weighing 
should  not  be  more  than  half  a  milligram  different  from  the 
first. 

N.B. — It  is  frequently  recommended  that  the  CaCO.,  obtained  in  this 
manner  be  moistened  with  ammonium  carbonate  solution,  and  re-heated 
before  weighing.  This  is  to  bring  back  any  CaO  which  may  have  been 
formed  to  CaCOg.  Any  additional  accuracy  gained  by  this  method  is 
more  than  made  up  for  by  the  chances  of  loss  by  spirting. 

46.  When  the  weight  of  the  CaCO;^  has  been  verified,  the 
dish  may  be  placed  in  a  Fletcher  muffle  furnace  and  kept  at 


47-50]  Estimation  of  Calcium  31 

a  bright  red  heat  for  twenty  minutes,  cooled  in  a  desiccator, 
and  weighed  again.     This  gives  the  weight  as  CaO. 

When  only  small  quantities  of  lime  are  to  be  estimated  (less 
than  -I  gram),  the  CaO  method  should  be  used.  For  larger 
quantities  the  CaC03  method  is  sufficiently  accurate. 

47.  Calculation. — The  calculation  is  very  simple;  it  is 
either 

Wt  ofCaCO^x^o^  O^ 

Wt.  of  spar  taken 


or 


Wt.    of  CaO    X    100  ^         cr^    r^ 

■117.: — r ^z~^ =  %  of  CaO. 

Wt.  of  spar  taken        /" 


ESTIMATION   OF   CARBON   DIOXIDE   IN 
CARBONATES 

48.  Substance  used. — Iceland  spar,  CaC03. 
Methods.— («)  By   difference.     The   carbon   dioxide   is 

driven  off  by  means  of  an  acid,  and  the  loss  of  weight  caused 
thereby  is  estimated 

{b)  By  direct  weighing.  The  carbon  dioxide  given  off  on 
treatment  with  an  acid  is  absorbed  and  weighed. 

49.  {a)  This  method,  although  capable  of  giving  very  good 
results  in  the  hands  of  a  skilled  analyst,  is  somewhat  difficult 
for  a  student.  Still,  since  it  is  frequently  used  both  in  com- 
mercial practice  and  in  technical  examinations,  it  is  well  that 
the  agricultural  student  should  be  familiar  with  it. 

Several  kinds  of  apparatus  are  used  for  this  determination, 
but  all  are  the  same  in  principle.  Two  are  described  ;  one 
which  is  readily  fitted  up  in  any  laboratory,  and  a  second  which 
must  be  made  by  a  professional  glass  blower,  but  which  is 
obtainable  from  any  manufacturing  firm. 

50.  Apparatus  required.— i.  The  apparatus  is  readily 


32     Estimations  occurring  in  Agricultural  Analysis     [51 


Fig,  20, 


understood   from    fig.    20.      A    wide-moulhed   4-oz.    flask   is 

fitted  with  an  india-rubber  stopper,  through  which  are  bored 

two  holes.     Through  one  is  fitted  a 

tube,    A  A,    reaching    close   to    the 

bottom   of  the   flask  \   through  the 

other  is   placed   another  tube,  b  b, 

which   terminates   at   one    end  just 

inside  the  stopper  and  at  the  other* 

after  being  bent  three  times  at  right 

angles,   inside    a    calcium    chloride 

tube,  c.     The  outer   ends  of  these 

two  tubes  are  closed    by  pieces   of 

india-rubber   tubing,  into   which  fit 

stoppers  of  glass  rod. 

The  apparatus  is  completed  by  placing  a  portion  of  a  teSt 
tube,  E,  inside  the  flask.  This  must  be  just  so  long  that  it 
cannot  lie  down  in  the  flask,  but  so  short  that  the  india-rubber 
stopper  may  be  inserted  without 
touching  it. 

The  tube  c  is  filled  with  small 
pieces  of  fused  calcium  chloride, 
and  the  test  tube,  e,  is  filled  three- 
quarters  full  of  hydrochloric  acid,  i 
part  strong  acid  and  i  part  distilled 
water,  and  the  apparatus  is  ready 
fOr  use. 

51.  Schroeder's  Apparatus. 
— 2.  Should  this  form  be  used,  the 
cistern  ^,  fig.  21,  is  filled  with  hydro- 
chloric acid  I  to  I,  and  the  cis- 
tern c  is  half  filled  with  strong  sulphuric  acid,  which  dries  the 
effluent  gas  just  as  the  calcium  chloride  does  in  the  first 
apparatus.     The  apparatus,  whichever  of  the  two  it  may  be, 


>^5^ 


Fig.  21. 


52-54]  Estimation  of  Carbon  Dioxide  33 

is  first  of  all  weighed,  care  being  taken  that  no  moisture 
adheres  to  its  exterior.  About  i  gram  of  finely  ground  Iceland 
spar  is  then  introduced  into  the  apparatus,  and  it  is  weighed 
again,  the  difference  giving  the  weight  of  spar  added. 

If  the  first  apparatus  be  used,  care  must  be  taken  that  none 
of  the  added  substance  fall  into  the  test  tube  of  acid.  To 
avoid  this  it  is  desirable  to  remove  the  tube  whilst  pouring  the 
substance  into  the  flask.  If  Schroeder's  apparatus  be  used,  the 
carbonate  may  be  poured  through  the  opening  d. 

The  next  operation  is  to  drive  off  the  carbon  dioxide. 

52.  If  the  apparatus  in  fig.  20  be  used,  f  is  unstoppered, 
and  the  flask  is  tilted  on  one  side  so  as  to  allow  the  acid  in  e 
to  run  over  on  to  the  substance  below.  As  soon  as  effervescence 
ceases  a  little  more  acid  is  run  over.  This  operation  is  con- 
tinued until  the  whole  of  the  substance  is  dissolved.  The 
flask  is  then  placed  on  top  of  the  water  oven  for  about  ten 
minutes  to  expel  any  CO 2  which  may  be  dissolved  in  the 
liquid.  Finally,  the  stopper  at  a  is  removed,  and  air  slowly 
aspirated  through  the  apparatus  (by  attaching  f  to  an  air-pump 
or  by  sucking  a  tube  attached  to  f)  until  all  CO2  is  expelled 
from  the  flask.  The  stoppers  at  a  and  f  are  then  replaced, 
and  the  apparatus  is  weighed. 

53.  Calculation.— 

Weight  I.       =  Apparatus. 
Weight  II.     =  Apparatus  -f  Substance. 
Weight  III.  =  Apparatus  -f-  Substance  —  CO2. 
.*.  Weight  II.  —  Weight  I.      =  Iceland  spar, 
and  Weight  II.  -  Weight  III.  =  COg. 

From  this  the  percentage  of  CO2  in  the  Iceland  spar  may 
be  readily  calculated. 

54.  If  Schroeder's  apparatus  be  used,  the. acid  is  let  in 
gradually  as  before  by  the  tap  at  the  bottom  of  the  cistern  ^, 

D 


34    Estimations  occurring  in  Agricultural  Analysis    \bb 

and  the  CO2  evolved,  after  bubbling  through  the  H2SO4  in  r, 
is  allowed  to  escape  into  the  air.  The  apparatus  is  warmed 
and  the  air  expelled  as  before,  the  stopper  and  tap  on  b  of 
course  being  opened.  The  apparatus  is  then  weighed,  and 
the  percentage  of  CO2  calculated  as  before. 

55.  Method  b.    By  direct  weighing.— Several  forms 
of  apparatus  are  used  for  this  estimation,  perhaps  the  simplest 


Fig.  22. 


being  that  recommended   in   Crookes's    '  Select   Methods   of 
Chemical  Analysis.'  ^ 

'  For  the  benefit  of  those  who  wish  to  try  this  method,  I  quote  the 
following  : 

H.  T.  S.  Gladding  uses  an  apparatus  for  the  estimation  of  carbonic 
acid  by  absorption.  It  consists  of  the  ordinary  generating  flask,  followed 
by  an  empty  U  tube  to  retain  condensed  water  vapour  ;  this  is  succeeded 
by  four  potash  bulbs  of  the  Geissler  form.  The  first  of  these  contains 
concentrated  sulphuric  acid  to  dry  the  gas.  The  next  two  contain  potash 
solution  of  Sp.  G.  i  '27  for  absorbing  the  carbonic  acid  ;  the  last  contains 
concentrated  sulphuric  acid  to  absorb  the  moisture  given  up  by  the  potash 


55] 


Estimation  of  Carbon  Dioxide 


35 


For  use  by  students,  however,  the  apparatus  shown  in  fig.  22 
is  to  be  recommended. 

a  is  an  8-oz.  conical  flask,  into  which  the  weighed  quantity 
of  carbonate  is  placed.  Through  the  stopper  of  the  flask  pass 
two  tubes,  one  communicating  with  a  reservoir  of  dilute  hydro- 
chloric acid,  b^  and  the  other  with  a  series  of  tubes,  d^  e,  / 
and  g,  intended  to  purify  and  absorb  the  CO^  formed. 

At  the  end  of  this  series  of  tubes  is  some  form  of  aspirator, 
by  means  of  which  a  current  of  pure  dry  air  may  be  caused  to 
pass  through  the  whole  apparatus. 

Preparation  of  the  apparatus  : 

First  of  all,  the  different  U  tubes  must  be  carefully  cleaned 
and  filled  as  follows  : 

Tube  f     This  is  the  tube  which  is  destined  to  absorb  the 
CO2  evolved  in  the  flask  a.     The  form  of  tube  shown  in  the 
figure   is   very   convenient,  as  the   two 
stopcocks  enable   the  operator   to  shut 
off    its    contents    from    the    air    whilst 
weighing.     When  the  tube  is  perfectly 
clean  and  dry,  a  loose  plug  of  cotton 
wool  is   pushed   down  one  side  to  the 
position  I,  fig.   23.     The  part  3,  fig.  23, 
is  filled  with  granulated  soda  lime  which 
has  been  sifted  free  from  dust,  and  the 
part   2,  fig.  23,    with   granular   calcium 
chloride.    Two  little  plugs  of  cotton  wool 
are  then  placed  at  the  ends,  4,  4,  fig.  23,  and  the  glass  stop- 
cocks inserted. 


Fig,  23. 


solution.     Then  comes  a  U  tube  containing  soda-lime,  and  serving  as  a 
guard. 

The  last  three  Geissler  bulbs  constitute  the  weighable  portion  of  the 
apparatus.  Perfectly  dry  air  plus  carbonic  acid  enters  these,  and  perfectly 
dry  air  alone  escapes.  The  increase  in  weight  gives  the  amount  of  car- 
bonic acid. 

D2 


36   Estimations  occurring  in  Agricultural  Analysis    [55 

Tube  e.  This  tube  must  have  a  plug  of  cotton  wool  driven 
down  until  it  divides  the  tube  into  equal  portions.  One  limb 
is  filled  with  granulated  CaCl2,  and  the  other  with  small 
pieces  of  pumice  which  have  been  soaked  in  a  saturated  solu- 
tion of  CUSO4,  then  dried  at  200°  C.  until  they  have  become 
colourless. 

Tube  g  is  filled  with  CaCl2.  The  remaining  tube  (c)  is  to 
purify  the  air  which  is  passed  through  at  the  end  of  the  opera- 
tion. It  is  filled  with  soda  lime.  When  all  the  different  pieces 
of  apparatus  shown  in  the  figure  have  been  got  together,  the 
Liebig's  bulbs  {d)  must  be  filled  about  half  full  of  strong  sul- 
phuric acid,  and  the  absorption  tubes  joined  together  with  india- 
rubber  tubing.  Especial  care  must  be  taken  that  the  different 
reagents  with  which  the  CO2  comes  in  contact  after  leaving  the 
flask  are  arranged  in  the  correct  order,  as  it  is  very  easy  'to 
get  some  of  the  tubes  turned  the  wrong  way  round.  The 
correct  order  is  as  follows  : 

Strong  sulphuric  acid  to  dry  the  gas,  and  contained  in  the 
bulbs  d. 

Calcium  chloride  to  complete  this  drying,  and  contained  in 
the  limb  of  e  next  the  bulbs. 

Anhydrous  copper  sulphate  and  pumice,  to  absorb  any  HCl 
which  may  come  over,  and  contained  in  the  limb  of  e  next  to/ 

Soda  lime  to  absorb  the  CO2,  contained  in  the  limb  of  / 
next  to  e. 

Calcium  chloride,  contained  in  the  limb  of  /  next  to  g. 
When  the  soda  lime  begins  to  absorb  CO2  it  gets  warm  and 
loses  a  little  moisture.  This  CaCl2  is  to  absorb  any  such 
moisture. 

Calcium  chloride,  contained  in  ^,  to  prevent  any  moisture 
from  diffusing  back  into/ 

Having  made  the  absorption  apparatus  and  got  it  correctly 
in  position,  the  pipette,  b,  is  fitted  into  the  stopper  so  that  its 


56,  57]  Estimation  of  Carbon  Dioxide  37 

tip  reaches  nearly  to  the  bottom  of  the  flask  a.  Above,  the 
pipette  is  joined  to  the  tube  c  by  about  6  inches  of  india- 
rubber  tubing  which  is  closed  by  a  clip. 

56.  The  Determination.— Weigh  about  a  gram  of  the 
pure  Iceland  spar,  and  transfer  it  to  the  flask  a.  Next  weigh 
the  tube  /  and  replace  it  in  its  position.  Fill  the  tube  b  with 
dilute  hydrochloric  acid,  and  close  the  clip  so  that  no  acid 
may  drop  from  the  tip  of  the  pipette.  Replace  the  stopper  in 
the  flask,  and  the  whole  apparatus  will  appear  exactly  as  in  the 
figure,  excepting  that  the  aspirator  will  not  be  in  position. 
Loosen  the  clip  above  ^,  so  that  the  acid  may  flow  down  slowly 
upon  the  spar.  When  all  eflervescence  has  ceased,  close  the 
clip  and  bring  the  acid  to  a  boil  by  placing  a  Bunsen  beneath 
it  ;  next,  lower  the  flame,  attach  g  to  the  aspirator  or  to  a 
pump  (fig.  15),  loosen  the  clip,  and  allow  air  to  pass  through 
the  apparatus  for  fifteen  minutes.  The  speed  of  the  air  current 
should  be  so  regulated  that  the  bubbles  may  be  counted  as 
they  pass  through  the  sulphuric  acid  bulb.  When  the  air 
has  been  passing  for  the  prescribed  time,  stop  the  aspirator, 
turn  ofl"  the  stopcocks  in  /,  and  remove  the  tube  :  weigh  it. 
The  amount  which  it  has  gained  will  represent  the  amount  of 
CO2  which  has  been  given  off  from  the  spar. 


Section  II.— VOLUMETRIC  ESTIMATIONS 

57.  In  w/2^w^/r/V  analysis  the  balance  is  to  a  great  extent 
replaced  by  instruments  which  measure  volumes. 

The  principle  of  volumetric  analysis  is  best  explained  by 
taking  an  example.  Suppose  that  we  had  a  solution  of  sul- 
phuric acid  of  which  we  knew  the  exact  strength,  every  c.c. 
containing  a  certain  weight  of  pure  H2SO4.  It  is  required  by 
means  of  this  solution  to  find  out  how  much  pure  KHO  exists 


38    Estimations  occurring  in  Agricultural  Analysis    [58 

in  a  solution  of  this  substance.  The  method  would  be  to 
measure  out  a  quantity  of  the  KHO  solution,  mix  with  it  a 
few  drops  of  litmus  solution,  and  add  the  sulphuric  acid  until 
the  liquid  became  neutral. 

If  we  could  measure  the  volume  of  H2SO4  solution  added, 
we  should  know  the  weight  of  pure  H2SO4  required  to  neutra- 
lise the  KHO  in  the  KHO  solution.  From  the  weight  of 
H2SO1  it  would  be  easy  to  calculate  the  weight  of  KHO. 

A  solution  of  known  strength,  such  as  the  sulphuric  acid  in 
the  above  example,  is  called  a  standard  solution. 

A  substance  which  tells  when  the  reaction  is  completed,  as 
the  litmus  in  the  example,  is  called  an  indicator. 

The  instrument  by  which  the  amount  of  sulphuric  acid  is 
added  is  a  burette. 

58.  Standard  Solutions. — For  convenience  in  calcu- 
lating, standard   solutions  are  generally  made   up   to   certain 

strengths  known  as  normal  (N),  seminormal  (  —  ] ,  and  deci- 
normal    I  —  ] . 

A  normal  solution  of  a  monobasic  acid^  or  of  a  monacidic 
alkali,  is  one  of  which  i  litre  contains  the  molecular  weight 
in  grams  of  the  acid  or  alkali. 

A  normal  solution  of  any  other  acid  is  one  of  which  i  litre 
will  exactly  neutralise  i  litre  of  normal  monacidic  alkali  solu- 
tion. In  the  same  way,  a  normal  solution  of  any  other  alkali 
would  be  one  of  which  i  litre  will  exactly  neutralise  i  litre  of 
normal  monobasic  acid  solution.  Thus,  a  litre  of  a  normal 
solution  of  caustic  potash,  KHO,  would  contain  56  grams  of 
potash,  and,  according  to  the  equation 

HCl  +  KHO  =  KCH-H2O 
36-5+    56     =  74'5  +  i8, 

a  litre  of  normal  potash  would  exactly  neutralise  36*5  grams 


59]  Volumetric  Estimations  39 

of  HCl,  and  if  this  amount  be  made  up  to  a  litre  with  water 
it  will  constitute  a  normal  solution  of  HCl. 

On  the  other  hand,  should  a  dibasic  acid  be  used,  only 
half  its  molecular  weight  will  be  required  to  make  a  litre  of 
normal  solution,  as  may  be  seen  from  the  equation 

H2SO4  +  2KHO  =  K2SO4  +  2H2O 
98    +  56x2  =     135    +2x18 

Ninety-eight  grams  (or  the  molecular  weight  in  grams)  of 
H2SO4  will  neutralise  56x2  grams  of  KHO,  or  2  litres  of 
normal  KHO. 

In  the  same  way,  a  normal  solution  of  oxalic  acid, 
C2H2O4.2H2O,  will  contain  126-^-2,  or  63  grams  per  litre. 

As  normal  solutions  are  often  too  strong  for  delicate  work, 
solutions  of  half  normal  strength  (seminormal),  or  one-tenth 
normal  strength  (decinormal),  are  frequently  used. 

Very  little  practice  will  soon  show  the  student  that  the  great 
advantage  which  solutions  of  normal  strength,  or  some  simple 
fraction  of  this  strength,  have  over  all  others  is  in  the  facility 
with  which  results  may  be  calculated  from  them. 

59.  Indicators. — The  following  are  the  principal  indi- 
cators used  : 

Litmus.  The  solution  is  not  often  used  in  agricultural 
work,  but  litmus  paper  is  sometimes  necessary.  This  is  bought 
in  small  strips  made  up  into  the  form  of  books,  and  will  be 
familiar  to  students  who  have  done  any  qualitative  analysis. 

Cochineal  This  indicator  is  not  affected  in  colour  by 
carbonic  acid.  It  may  be  prepared  by  dissolving  i  gram  of 
powdered  cochineal  in  20  c.c.  of  methylated  spirit,  diluting 
with  80  c.c.  of  water,  and  allowing  to  settle.  The  clear  liquid 
is  yellow,  but  is  changed  to  a  deep  wine-red  by  alkalis.  It 
should  not  be  used  in  presence  of  iron,  aluminium,  or  acetic 
acid,  or  their  compounds. 


40    Estimations  occurring  in  Agricultural  Analysis   [60 

Phenol'phthalein.  Must  be  dissolved  in  alcohol.  Colour- 
less when  acid  or  neutral  red  when  alkaline.  It  should  not  be 
used  with  ammonia,  but  is  very  useful  in  the  titration  of  weak 
organic  acids. 

Lacmoid.  Dissolves  in  water,  and  gives  the  same  colour 
effects  as  litmus,  but  is  more  sensitive. 

Methyl  orange.  Is  a  most  convenient  indicator  and 
strongly  to  be  recommended,  its  colour  being  bright  yellow  with 
alkalis  and  red  with  acids.  It  should  be  made  up  by  dissolving 
a  gram  in  a  litre  of  water.     It  is  not  aftected  by  carbonic  acid. 

In  using  indicators  to  determine  the  end  of  a  reaction,  the 
solutions  should  always  be  used  in  the  same  way.  For  in- 
stance, if  methyl  orange  be  used  to  determine  when  a  certain 
amount  of  H2SO4  is  neutralised  by  running  in  alkali  from  a 
burette,  a  slightly  different  result  will  be  obtained  from  that 
which  would  be  got  by  running  the  acid  into  the  alkali. 

PREPARATION  OF  SEMINORMAL  SULPHURIC 
ACID 

60.  Half  fill  a  litre  flask  with  distilled  water.  Measure  out 
35  c.c.  of  strong  sulphuric  acid  in  a  graduated  loo-c.c.  cylinder, 
and  pour  it,  a  little  at  a  time,  into  the  water  in  the 
flask,  shaking  the  liquid  round  after  each  addition. 
The  acid  need  not  be  measured  very  exactly,  as 
the  solution  has  to  be  standardised  afterwards. 
When  all  the  acid  has  been  added,  cool  the  flask, 
either  by  allowing  it  to  stand  over  night  or  by 
placing  in  a  current  of  cold  water,  as  shown  in  fig.  , 
24.     The   beaker  placed  over   the    mouth   of  the 

Fig.  24.  ^  ^  ,         , 

flask  prevents   any  water   getting  into  the  liquid. 
Next  fill  up  to  the  litre  mark  with  water,  and  mix  thoroughly. 

N.B. — When  large  quantities  of  standard  acid  have  to  be  prepared, 
this  mixing  becomes  a  matter  of  some  difficulty.     The  best  method  is  to 


61,  62]  Seminormal  Sulphuric  Acid  41 

pour  the  liquid  into  a  large  bottle,  and  force  a  rapid  stream  of  air  through 
it.     This  may  be  done  by  means  of  the  blowpipe  bellows. 

61.  Standardising. — Carefully  clean  a  burette,  washing  it 
first  with  distilled  water,  then  with  a  portion  of  the  acid  which 
has  just  been  made  up.  Allow  it  to  drain  for  a  minute,  then 
fill  it  with  the  acid.  Drop  an  Erdmann's  float  into  the  top  of 
the  burette,  and  allow  the  liquid  to  run  from  the  tap,  or  pinch- 
cock,  until  the  mark  on  the  float  stands  at  the  o  c.c.  mark  on 
the  burette.  Now  allow  exactly  10  c.c.  to  run  out  into  a  clean 
12-0Z.  beaker;  dilute  to  about  50  c.c,  and  determine  the 
amount  of  H2SO4  exactly  as  described  in  paragraphs  28  to  30. 
As  soon  as  this  is  started,  take  another  10  c.c.  from  the  burette, 
and  make  a  duplicate  determination  in  the  same  way.  Should 
the  two  determinations  agree  pretty  closely,  then  their  mean 
may  be  taken  as  the  true  quantity  of  H2SO4  contained  in  10  c.c. 
of  the  solution.  The  next  thing  is  to  calculate,  from  this  result, 
how  much  water  must  be  added  to  make  the  solution  exactly 
seminormal. 

62.  A  normal  solution  (see  paragraph  58)  contains  49  grams 
of  pure  H2SO4  ^  per  litre.      Therefore  a  seminormal  solution 

such   as  is  being   prepared,    should  contain  --2  =  24-5  grams 

2 

per  litre,  or  -245  gram  per  10  c.c. 

Now,  by  experiment   we   have   found   how  much  H2SO4 
10  c.c.  of  our  solution  contains.     Call  this  x. 

If  X  grams  of  H2SO4  are  contained  in  10  c.c, 
then   I  gram  ,,         is  ,, 

.*.  -245  gram  ,,         is  ,, 


10 

—      >> 
X 

5 

•245  X 

10 

.2-45 

X 

X 

*  On  page  23  a  method  was  described  for  the  estimation  of  sulphuric 
acid,  where  the  result  was  calculated  as  SO3.  The  use  of  the  formula 
HgSO^  in  volumetric  and  of  the  anhydride  SO3  in  gravimetric  analysis  is 
merely  a  matter  of  convenience  which  will  be  better  understood  by  the 


42  Estimations  occurring  in  Agricultural  Analysis  [63,  64 

If,   therefore,  we  wish   to  have  our   acid  seminormal,  we 

must  dilute  every  -"^-^   c.c.    until    it    becomes    lo    c.c.  ;    or, 

X 

multiplying  these  quantities  by  loo,  we  must  dilute   '^^^  c  c. 

X 

to  a  litre. 

To  do  this  pour  the  calculated  quantity  of  the  dilute  acid 

(^^   c.c.)    into   a   stoppered,  graduated   litre   cylinder,  and 

fill  up  to  the  litre  mark  with  distilled  water.  Mix  well  by 
shaking.  The  solution  so  prepared  should  be  accurately 
seminormal. 

Keep  this  standard  solution  in  a  well-stoppered  Winchester 
quart  bottle,  taking  care  that  it  is  quite  clean  and  dry  before 
pouring  in  the  liquid.  If  it  be  not  quite  dry,  wash  it  out  with 
a  little  of  the  standard  acid ;  throw  away  the  washings,  then 
pour  in  the  rest  of  the  acid. 

PREPARATION  OF  SEMINORMAL  CAUSTIC 
POTASH  SOLUTION 

63.  Weigh  out  on  a  rough  balance  10  grams  of  solid  caustic 
potash  ;  place  this  in  a  20-oz.  beaker,  together  with  about 
300  c.c.  of  distilled  water,  and  allow  it  to  dissolve.  When  all 
the  solid  has  disappeared,  pour  the  liquid  into  a  clean  litre  flask 
and  make  up  to  the  litre  mark  with  distilled  water.  Caustic 
potash  gives  out  considerable  heat  on  dissolving,  so  that  the 
solution  will  be  distinctly  warm.  Before  proceeding  farther  it 
must  be  cooled  (fig.  24).  After  cooling,  the  solution  will  be 
found  to  have  shrunk  slightly.  Make  up  again  to  the  litre 
mark,  and  mix  thoroughly. 

64.  Standardisation. — Fill   a   burette   with  seminormal 

student  when  calculating  the  results  of  the  more  complex  analyses  de- 
scribed later  on. 


65]  Seminormal  Caustic  Potash  Solution  43 

sulphuric  acid,  as  described  in  the  last  article,  and  another  with 
the  caustic  potash  solution  just  prepared.  Run  out  10  c.c.  of 
the  acid  into  an  8-oz.  beaker.  Stand  the  beaker  on  a  white 
tile  under  the  KHO  burette;  add  a  drop  of  methyl  orange 
solution  (paragraph  59),  stir  with  a  glass  rod,  and  run  the  alkali 
solution  from  the  burette,  drop  by  drop,  into  the  beaker,  stir- 
ring continually  until  the  colour  changes  from  red  to  yellow. 
When  the  solution  is  just  neutralised  one  drop  of  alkali  should 
make  the  change  from  red  to  yellow.  Read  off  the  amount  of 
alkali  used  and  repeat  the  experiment  several  times.  Take 
the  mean  of  your  readings  as  accurate. 

The  next  operation  is  to  dilute  your  solution  to  seminormal 
strength. 

Suppose  that  the  amount  of  alkali  which  neutralises  10  c.c. 

of  -  H2SO4  is  X. 

2 

Then  x  c.c.  must  be  diluted  to  10  c.c,  or  loo:^!:  c.c.  must 
be  diluted  to  a  litre. 

Measure  out  in  a  graduated  litre  cylinder  ioo:\:  c.c.  of  alkali 
solution.  Make  up  to  a  litre  with  distilled  water,  shake  up  well 
and  store  in  a  clean  well-stoppered  Winchester  quart  bottle. 

The  solution   should  now  be   seminormal — i.e.^  it  should 

contain  ^  grams  of  KHO  per  litre. 
2 

A  fresh  experiment  should  be  made  with  this  seminormal 

solution  to  see  that  10  c.c.  of  the  —  sulphuric  acid  is  exactly 

2 

N 
neutralised  by  10  c.c.  of  the  —  alkali. 

65.  The  two  solutions  whose  preparation  has  just  been 
described  are  used  very  largely  in  the  estimation  of  nitrogen 
(see   Part  III.).     Greater  accuracy  is,  however,  obtained  by 

using   a   —   solution  of  caustic  potash.     To  prepare  this  it  is 


44  Estimations  occurring  in  Agricultural  Analysis  [66,  67 

only  necessary  to  measure  out  200  c.c.  of  the  seminormal 
solution  into  a  litre  flask  and  fill  up  to  the  mark  with  water. 
Of  course  the  new  solution  must  be  thoroughly  mixed.  The 
seminormal  solution  of  H2SO4  is  of  very  convenient  strength 
for  nitrogen  estimations,  so  that  it  must  be  remembered  that 

50  c.c.  potash  solution  correspond  to  20  c.c.  sulphuric 
acid  solution. 

ESTIMATION  OF  CHLORINE  IN  SOLUBLE 
CHLORIDES 

66.  Method. — A  solution  of  silver  nitrate  is  made  of 
known  strength,  and  the  volume  required  to  precipitate  the 
whole  of  the  chlorine  as  AgCl  is  noted. 

67.  Preparation  of  Standard  Silver  Nitrate  So- 
lution.— Two  watch  glasses  having  ground  edges  and  a  clip 
are  weighed,  and  into  one  of  them  is  introduced  as  nearly 
as  possible  17  grams  of  powdered  pure  silver  nitrate.  This 
watch  glass  is  then  placed  in  the  steam  oven  for  half-an- 
hour,  allowed  to  cool  in  a  desiccator,  and  then  clipped  to 
the  other  watch  glass.  The  two  watch  glasses,  with  clip 
and  dry  nitrate  of  silver,  are  then  weighed  accurately.  A 
glass  filter  funnel  is  placed  in  the  neck  of  a  graduated  litre 
cylinder.  The  clip  is  taken  off  the  watch  glasses,  and  the 
silver  nitrate  is  washed  with  cold  water  down  the  funnel  into 
the  cylinder.  The  glasses  and  funnels  are  well  washed  to  free 
them  from  any  adhering  silver  nitrate,  and  the  washings,  which 
should  not  exceed  300  c.c,  allowed  to  run  into  the  cylinder. 
The  solution  is  left  standing  until  all  the  solid  is  dissolved. 
The  cylinder  is  then  filled  up  to  the  looo-c.c.  mark  with 
distilled  water. 

If  exactly  1 7  grams  have  been  taken,  then  the  solution  will 
be  decinormal  j  but  if  it  should  be  more  or  less,  then  a  certain 


68,  69]  Estimation  of  Chlorine  45 

factor  will  have  to  be  used  with  it — that  is  to  say,  the  number 
of  c.c.  used  in  any  operation  will  have  to  be  multiplied  by 
a  number  or  factor  to  tell  us  how  many  c.c.  would  have  been 
used  had  the  solution  been  accurately  decinormal. 

This  must  be  calculated  from  the  weight  taken  in  the 
following  manner  : 

Suppose  the  actual  weight  taken  to  have  been  i6'9545 
grams. 

Now,  17  grams  AgNOg  are  contained  in  1000  c.c.    -  AgNOs, 

10 


I  gram     „         is 


1000 

55 


17 


and  16-9545  grams  AgNOg  are     „  logo  x  16-9545  ^^ 

17 
This  fraction  works  out  to  997-3. 

But  16-9545  grams  AgNOj  are  contained  in  1000  c.c.  of  our  solution, 

N 
.*.  1000  c.c.  of  our  solution  =  997 '3  — AgNOg, 

or  I  c.c.       ,,         „         =-9973  .» 

That  is  to  say,  if  we  multiply  the  number  of  c.c.  of  our 
solution  used  in  any  operation  by  '9973,  the  product  will  be 
the  number  of  c.c.  which  would  have  been  used  had  the  solu- 
tion been  decinormal.  Therefore  '9973  is  the  factor  for  this 
solution. 

68.  Potassic  Chromate  Solution.— A  2  per  cent,  so- 
lution of  pure  neutral  potassic  chromate  is  made.  This  should 
be  perfectly  free  from  chlorine.  It  may  be  tested  by  adding  a 
drop  of  nitric  acid  to  a  small  quantity,  and  then  a  drop  of  silver 
nitrate  solution.  If  it  remains  perfectly  clear,  chlorides  are 
absent. 

69.  The  Estimation.  —  Weigh  out  accurately  about 
I  gram  of  pure  common  salt  (NaCl)  into  a  small  beaker;  dis- 
solve this  in  50  c.c.  of  cold  water,  transfer  into  a   250-c.c. 


46    Estimations  occurring  in  Agricultural  Analysis   [70 

measuring  flask,  rinsing  out  the  beaker  well  with  cold  distilled 
water  and  adding  the  rinsings  to  the  solution  in  the  flask. 
Fill  up  with  distilled  water  to  the  mark,  and  shake  up  the 
solution  so  as  to  mix  thoroughly.  Measure  out  25  c.c.  of  this 
solution  with  a  pipette  into  an  8-oz.  beaker,  and  add  one 
drop  of  the  K2Cr04  solution. 

Fill  up  a  burette  with  the  standard  silver  nitrate  solution, 
add  an  Erdmann's  float,  taking  care  that  there  are  no  bubbles 
of  air  either  attached  to  the  float  or  in  the  stopcock.  Note 
the  position  of  the  mark  on  the  float.  Stand  the  beaker 
containing  the  NaCl  on  a  white  tile,  and  allow  the  silver  solu- 
tion to  run  into  it,  drop  by  drop,  stirring  continuously  with  a 
glass  rod.  As  each  drop  of  AgNOg  enters  the  liquid  in  the 
beaker  a  bright-red  precipitate  of  Ag2Cr04  is  momentarily 
formed,  but  this  immediately  becomes  white  as  it  is  turned  by 
the  salt  into  AgCl.  When  the  white  precipitate  begins  to 
curdle  and  settle,  add  the  AgNOg  more  slowly,  stirring  after 
each  drop  until  the  red  colour  entirely  disappears.  As  soon 
as  the  red  colour  remains  permanent,  leaving  the  solution  just 
faintly  coloured,  close  the  stopcock  of  the  burette  and  note 
down  the  new  position  of  the  float.  The  difference  between 
the  two  positions  gives  the  amount  added.  Make  two  or 
three  determinations  in  this  manner,  using  the  mean  of  your 
readings  as  the  true  result. 

70.  Calculation. — First  multiply  the  factor  by  the  number 
of  c.c.  used.  This  will  give  the  number  of  c.c.  which  would 
have  been  used  had  the  solution  been  decinormal — ie,y  had  it 
contained  17  grams  of  AgNOg  or  10 -8  of  Ag  per  litre.  By 
inspecting  the  equation 

Ag  +         CI  =        AgCl 

108         +         35-5  =         i43'5 

we  see  that  108  of  silver  are  equal  to  35-5  of  chlorine, 


71,  72]  Estimation  of  Chlorine  47 

:,    -0108   Ag  precipitates   '00355  CI,   but   i   c.c.       AgNOg 

10 

contains  -0108  Ag   .%  we  multiply  the  number   of  c.c.  of — 

10 

AgNOs  used  by  '00355,  which  will  give  the  number  of  grams 
of  chlorine  in  the  25  c.c.  of  the  NaCl  solution;  this  multiplied 
by  10  gives  the  total  weight  of  chlorine,  and  this  multiplied 
by  100  and  divided  by  the  weight  of  NaCl  taken  gives  the  per- 
centage of  CI  in  the  NaCl  solution. 


VOLUMETRIC  ESTIMATION  OF  IRON 

71.  This  estimation  depends  upon  the  fact  that  ferrous 
salts  may  be  oxidised  by  either  KaMngOg  or  KgCrgO;  in  the 
presence  of  acids   to   ferric  salts   by   one   of  the  equations  : 

loFeSO,  +  K^MnPs  +  SH^SO^  =  5Fe2(SO,)3  +  2MnS0,  +  K2SO4  +  SHp. 
6FeS0,  +  K^Crp,  +  7H2SO4  =  sFe^CSOJg  +  Cr^CSOJg  +  K^SO,  +  7H2O. 

From  these  equations  it  will  be  seen  that  one  molecule  of 
K2Mn208  will  oxidise  ten  of  FeS04  or  316  grams  of  KaMngOg 
will  oxidise  10  x  56  grams  of  iron  from  the  ferrous  to  the 
ferric  state.  Thus  a  normal^  solution  of  KgMnaOg  would  con- 
tain 3 1  "6  grams  per  litre.  In  the  same  way  it  may  be  calcu- 
lated that  a  normal  solution  of  KaCrgO;  will  contain  49  grams 
per  litre. 

72.  Preparation  of  Standard  Bichromate  of 
Potash. — This  solution,  although  slightly  more  troublesome 
to  use  than  permanganate,  has  the  advantage  of  permanency. 
It  may  be  kept  in  a  well-stoppered  bottle  almost  indefinitely, 
without  suffering  any  change  of  strength. 

Weigh  out  exactly  4*91  grams  of  powdered  K.2Cr207  which 

'  It  will  be  noticed  that  the  word  normal  is  here  used  in  a  manner  which 
is  not  included  by  the  definition  given  on  page  38,  as  Kg^ngOs  is  neither 
an  acid  nor  an  alkali. 


48    Estimations  occurring  in  Agricultural  Analysis    [73 

has  been  dried  in  a  desiccator,  dissolve  in  water,  and  make  up 
to  a  litre  exactly  as  described  in  the  case  of  AgN03  '>  i^ix  well. 
73.  Estimation  of  Iron  in  Solutions  of  Ferrous  Salts. 
It  is  necessary  that  all  the  iron  in  the  solution  shall  be  in  the  fer- 
rous state.  If  any  ferric  salts  be  present,  they  must  be  reduced 
before  titration  as  described  in  the  next  article.  To  acquire 
proficiency  in  the  actual  estimation,  Fe(NH4)2(S04)2.6H20 
may  be  used.  Weigh  out  about  a  gram  of  this  salt,  dissolve 
it  in  water,  add  2  drops  of  strong  H2SO4,  and  make  up  to 
250  c.c.  in  a  flask  of  that  capacity.  After  shaking  up  well,  remove 
25  c.c.  with  a  pipette  into  a  beaker.  In  another  beaker  make 
up  a  very  dilute  solution  of  potassic  ferricyanide^  K3Fe(CN)c, 
by  dissolving  a  piece  of  this  salt,  about  the  size  of  a  hemp  seed, 
in  50  c.c.  of  distilled  water.  Place  about  a  dozen  separate  drops 
of  this  solution  on  a  white  tile.  This  is  most  easily  done  by 
dipping  a  glass  rod  into  the  solution  and  touching  the  plate 
with  it.  A  drop  of  any  acid  liquid  containing  iron  in  the 
ferrous  state  will  turn  one  of  these  drops  blue,  whilst  ferric  salts 
will  produce  no  visible  change. 

Warm  the  beaker  containing  the  ferrous  solution  to  about 
60°  C.  Run  in  the  decinormal  bichromate  solution  from  a 
burette,  half  a  c.c.  at  a  time,  stirring  well  after  each  addition. 
After  stirring,  take  out  a  drop  on  the  end  of  a  stirring  rod  and 
touch  one  of  the  K3Fe(CN)6  drops  on  the  tile.  As  soon  as 
no  colour  is  formed  read  off  the  amount  added.  This  gives 
a  rough  estimate  of  the  quantity  required ;  but,  seeing  that  we 
have  added  half  a  c.c.  at  a  time,  this  reading  may  be  -4  c.c. 
out,  as  the  liquid  is  apt  to  absorb  oxygen  from  the  air.  Throw 
away  the  liquid,  wash  out  the  beaker,  and  measure  out  another 
25  c.c.  Warm  up  to  about  60°  C.  as  before.  This  time  the 
bichromate  may  be  run  in  until  '5  c.c.  less  than  before  has 
been  added.  Then  add  the  solution,  drop  by  drop,  testing 
after   each  addition,   until   the   exact   amount   is   discovered. 


74-77]  Volumetric  Estimation  of  Iron  49 

Afterwards  check  your  work  by  taking  another  25  c.c.  and 
running  in  the  exact  amount,  all  but  a  drop  or  two,  finishing 
up  as  before 

74.  Calculation. — For  each  operation  one-tenth  of  the 
amount  of  ferrous  salt  weighed  out  has  been  used.  Therefore, 
the  total  amount  of  iron  in  the  250  c.c.  of  solution  is  obtained 
by  multiplying  in  10  x  "0056  by  the  number  of  c.c.  of  KgCrgO; 
used. 

75.  Estimation  of  Iron  in  Solutions  containing 
Ferric  Salts. — The  first  thing  necessary  is  to  reduce  the  iron 
to  the  ferrous  state.  Several  methods  have  been  devised  for 
performing  this  operation,  and  these  may  be  found  in  text 
books  on  general  quantitative  analysis.  The  one  here  given  is 
easily  and  rapidly  worked,  and  gives  good  results. 

76.  Make  up  a  solution  of  stannous  chloride  by  dissolving 
about  10  grams  of  the  salt  in  25  c.c.  of  hot  dilute  hydrochloric 
acid  (equal  parts  of  strong  acid  and  distilled  water),  dilute  to 
100  c.c,  and  keep  in  a  bottle  whose  stopper  is  very  slightly 
smeared  with  vaseline.  This  prevents  the  salt  from  creeping 
up  and  cementing  the  stopper  into  the  bottle.  It  will  not 
vitiate  the  solution,  because  that  is  always  taken  out  by  a 
pipette  as  shown  in  the  sequel.  A  few  pieces  of  pure  tin 
should  be  kept  at  the  bottom  of  the  liquid. 

Make  up  a  saturated  solution  of  mercuric  chloride  in 
100  c.c.  of  water. 

77.  The  Hstimation. — Measure  out  10  c.c.  of  a  dilute 
solution  of  ferric  chloride^  into  a  4-oz.  conical  flask,  add 
about  40  c.c.  of  water,  and  heat  to  boiling.  Suck  up  into 
a  5-c.c.  pipette  some  of  the  stannous  chloride  solution  and 
add  it,  drop  by  drop,  to  the  boiling  liquid  in  the  flask.  Con- 
tinue  adding    until    the    liquid    becomes    quite    colourless. 

'  If  it  be  desired  to  check  this  estimation  the  iron  should  be  deter- 
mined in  another  lo  c.c.  by  the  gravimetric  method  given  in  paragraph  22. 

E 


50  Estimations  occurring  in  Agricultural  Analysis  [78,  79 

Remove  the  flame,  and  add  i  c.c.  of  HgCl2  to  oxidise  the 
excess  of  SnCl2.  Boil  for  a  few  seconds.  If  the  operation 
has  been  carefully  conducted,  only  a  faint  precipitate  of 
HgaClg  will  be  formed.  Now  cool  down  the  flask,  by  running 
cold  water  round  it,  to  60°  C,  and  titrate,  exactly  as  with  the 
ferrous  salt,  using  the  whole  of  the  solution  in  the  flask  and 
making  a  separate  reduction  for  each  titration  until  the  exact 
quantity  of  bichromate  solution  required  is  found. 

78.  Permanganate  of  potassium,  as  before  stated,  may  be  substituted 
for  bichromate.  The  solution  of  this  substance  has  a  very  deep  purple 
colour,  and  as  that  colour  is  destroyed  by  reduction  no  indicator  is 
required. 

To  prepare  a  decinormal  solution  of  Y^^xi^^,  dissolve  about  5  grams 
of  this  substance  and  dilute  to  a  litre.  Standardise  it  by  means  of  oxalic 
acid  solution.     The  action  of  oxalic  acid  on  permanganate  is  as  follows  : 

SHoC.O^.aH^O  +  K^MnA  +  3H2SO, 


Dissolve  63  "Ol  grams  of  dry  crystals  of  oxalic  acid  in  water  and  make 
up  to  a  litre.  Measure  out  10  c.c.  into  a  beaker  by  means  of  a  pipette  ; 
add  5  c.c.  of  dilute  H2SO4  and  dilute  with  about  50  c.c.  of  water.  Heat 
this  solution  to  60°  C. ,  and  run  in  the  KjMngOg  solution  from  a  glass- 
tapped  burette,  stirring  after  each  addition.  As  soon  as  a  faint  permanent 
colour  is  produced,  read  off  the  amount  that  has  been  added.  From  this 
result  the  amount  of  K^Mn.^Og  per  c.c.  may  be  calculated. 

In  using  K^Mn^Og  solution  the  following  precautions  should  be  re- 
membered : 

Always  acidify  with  sulphuric  acid. 

No  HCl  must  be  present,  as  it  is  liable  to  be  oxidised  and  evolve  chlorine. 

Organic  matter  must  be  absent. 

Nitric  acid  should  be  present  only  in  very  small  quantities. 


ESTIMATION  OF  SUGAR 

79.  There  are  many  sugars  which  occur  in  the  vegetable  king- 
dom, but  in  this  article  only  two  are  dealt  with — viz.,  cane  sugar 
and  glucose.  All  the  determinations  which  have  been  described 
up  to  this  point  are  dependent  on  definite  chemical  reactions 


80]  Estimation  of  Sugar  5 1 

which  can  be  represented  by  equations  and  calculated  from 
atomic  and  molecular  weights.  The  determination  of  the 
quantity  of  sugar  in  any  substance  is  an  operation  of  a  different 
order.  No  calculation  can  be  made  from  equations.  The 
test  for  grape  sugar  known  to  elementary  students  (red 
precipitate  of  CugO  on  boiling  with  Fehling's  solution)  is  not 
strictly  quantitative,  as  a  slight  variation  of  the  conditions 
under  which  the  test  is  made  will  entirely  alter  the  results 
obtained.  Certain  sugars,  when  heated  with  an  alkaline 
solution  of  copper  tartrate,  give  red  precipitates  of  cuprous 
oxide.  The  quantity  of  that  precipitate  varies  greatly  not 
only  with  the  quantity  of  the  sugar,  but  also  with  its  chemical 
constitution  and  with  the  conditions  of  temperature  and 
strength  of  the  solution. 

It  is  therefore  evident  that  however  carefully  the  standard 
solution  of  copper  tartrate  may  be  made,  it  will  be  useless 
unless  carefully  standardised  by  the  especial  sugar  and  under 
the  especial  condition  of  temperature  and  dilution  which  will 
apply  when  the  actual  estimation  is  carried  out. 

The  two  sugars  dealt  with  in  this  article  are  cane  sugar  and 
glucose.  Glucose  is  estimated  by  the  method  described  below, 
but  cane  sugar  must  first  be  '  inverted '  by  boiling  with  an 
acid  which  converts  it  into  invert  sugar.  This  (dextrose 
and  laevulose)  has  practically  the  same  action  on  Fehling's 
solution  as  glucose  (dextrose). 

80.  Preparation  of  Fehling's  Solution.— Weigh  out 
exactly  34"64  grams  of  copper  sulphate  which  has  been  ground 
finely  and  pressed  between  folds  of  filter  paper.  Dissolve  with 
the  usual  precautions  in  about  300  c.c.  of  distilled  water,  prefer- 
ably in  a  500-c.c.  flask.  Make  up  to  the  500-c.c.  mark,  mix 
well,  and  keep  in  a  well-stoppered  bottle  marked  '  Fehling's 
solution  I.'  Next  weigh  out  173  grams  of  Rochelle  salt  (sodium 
potassium  tartrate)  and  160  grams  of  caustic  potash.     Dissolve 

£2 


52  Estimations  occurring  in  Agricultural  Analysis  [81,  82 

these  together  in  about  300  c.c.  of  water.  Decant  into  a 
500-c.c.  flask,  and  make  up  to  the  500-c.c.  mark.  Bottle  and 
label  '  Fehling's  solution  II.'  * 

81.  Preparation  of  Sugar  Solution.— Weigh  out 
exactly  2 '375  grams  of  pure  crystallised  cane  sugar.  Dissolve 
in  about  50  c.c.  of  water  in  a  beaker,  add  2  c.c.  of  dilute  HCl, 
and  place  the  beaker  on  the  water  bath  for  twenty  minutes. 
This  will  convert  the  cane  sugar  entirely  into  glucose.  Just 
neutralise  with  caustic  soda,  decant  into  a  500-c.c.  flask,  and 
wash  the  beaker,  pouring  the  washings  into  the  flask.  Make 
up  to  500  c.c.  and  mix  well.  If  this  solution  has  been 
correctly  made,  10  c.c.  will  contain  "05  gram  of  glucose,  which 
is  equivalent  to  '0475  of  cane  sugar. 

82.  Standardisation  of  Fehling's  Solution.— For 
this  purpose  the  sugar  solution  just  prepared  may  be  considered 
accurate.  In  fact,  for  the  reasons  set  forth  in  article  79  it  is 
far  more  likely  to  be  accurate  than  the  Fehling's  solution. 
Fill  two  burettes,  one  with  sugar  solution  and  the  other  with 
Fehling's  solution  I.  Place  the  burettes  in  clamps  which 
support  them  at  such  a  height  that  their  taps  are  about 
8  inches  above  the  bench.  Run  5  c.c.  of  solution  I.  into  an 
evaporating  basin  4  inches  in  diameter.  With  a  pipette  add 
5  c.c.  of  solution  II.  Stir  with  a  glass  rod  until  the  solution 
becomes  quite  clear,  then  place  the  basin  on  a  tripod  and 
heat  it  just  to  boiling.  It  is  most  convenient  to  have  a 
Bunsen  burner  about  a  foot  away  from  the  burette  containing 
the  sugar  solution.  This  enables  the  operator  to  slide  the 
tripod  with  the  basin  either  under  the  burette  or  over  the 
burner.     When  the  solution  boils,  slide  it  under  the  burette 

'  Fehling's  solution  II.,  like  all  other  strong  solutions  of  potash  and 
soda,  is  apt  to  give  trouble  by  fixing  the  stopper  of  the  bottle  tightly. 
This  difficulty  may  be  overcome  by  rubbing  the  stopper  lightly  with 
vaseline. 


82]  Estimation  of  Sugar  53 

and  run  in  5  c.c.  of  the  sugar  solution,  then  bring  it  back  over 
the  burner.  A  red  precipitate  will  form.  After  boiling  about 
thirty  seconds,  slide  away  from  the  fiame  and  allow  the 
precipitate  to  settle.  If  the  liquid  be  still  blue,  more  sugar 
must  be  added ;  if  colourless,  too  much  has  been  added 
already.  The  colc^r  of  the  liquid  is  best  seen  by  allowing  the 
precipitate  to  settle  completely,  and  then  tilting  the  basin  up 
sideways  so  that  the  white  side  of  the  basin  may  be  seen 
through  the  liquid.  In  this  case,  however,  the  liquid  will  be 
still  blue.  Add  another  c.c.  of  sugar  solution.  Boil  for  half- 
a-minute,  and  allow  to  settle  again.  Repeat  this  operation 
until  the  blue  colour  has  nearly  gone,  then  add  the  solution,  a 
drop  or  two  at  a  time,  boiling  after  each  addition  and  testing  a 
drop  of  the  liquid  for  copper  by  placing  it  on  a  porcelain  tile 
together  with  a  drop  of  potassium  ferrocyanide  solution  in 
dilute  HCl.  A  brown  colouration  shows  that  there  is  still 
excess  of  copper.  In  this  case  add  more  sugar,  boil,  and 
test  again. 

To  tell  when  the  reaction  is  complete  without  the  aid 
of  K4Fe(CN)6  requires  considerable  practice,  therefore  the 
student  is  advised  to  use  it  always. 

When  the  reaction  is  complete,  read  off  the  amount  of  sugar 
solution  which  has  been  added.  Now,  the  probability  is  that 
this  result  will  be  higher  than  the  truth.  The  reason  for  this 
may  be  seen  by  allowing  the  basin  to  stand  for  about  five 
minutes  after  the  determination  has  been  finished,  when  the 
solution  will  have  become  distinctly  blue  again  from  the  re- 
oxidation  of  the  CU2O. 

It  is  necessary,  therefore,  to  do  the  estimation  as  rapidly  as 
possible.  After  having  got  an  idea  of  the  quantity  which  is 
necessary  by  the  preliminary  operation  just  described,  clean 
out  the  dish,  take  a  fresh  5  c.c.  of  solution  I.  and  another  of 
solution   II.  as  before.     Mix  with  the  rod.     Heat  to  boiling, 


54  Estimations  occurring  in  Agricultural  Analysis  [83,  84 

and  run  in  the  requisite  amount  of  sugar,  all  but  '5  c.c.  Boil, 
and  see  whether  the  liquid  is  blue  ;  if  in  doubt,  test  with  acid 
K4Fe(CN)6.  Then  add  sugar,  drop  by  drop,  boiling  after  each 
addition  until  no  copper  is  left  in  solution.  Read  off  the 
result  again. 

A  third  determination  is  necessary  for  accuracy.  This  time 
run  in  the  whole  amount  of  sugar  solution  except  "i  c.c.  The 
operation  will  thus  be  done  very  rapidly,  and  hence  very  accu- 
rately.    Take  this  last  result  as  correct. 

When  the  Fehling's  solution  has  been  thus  standardised, 
calculate  what  weight  of  glucose  was  contained  in  the  quantity 
of  solution  used,  and  label  the  Fehling's  solution  bottles. 
Five  c  c.  solution  I.  and  5  c.c.  solution  II.  =  a:  glucose,  where 
X  is  the  weight  calculated. 

83.  It  has  already  been  pointed  out  that  different  results 
may  be  obtained  by  using  solutions  of  different  strength.  This 
necessitates  that  the  solution  we  work  with  shall  always  be  of 
nearly  the  same  strength  as  the  solution  used  in  standardising. 
Should  a  preliminary  determination  show  it  to  be  much 
stronger,  it  must  be  diluted  to  approximately  the  right 
strength. 

84.  Gravimetric  Method. — The  volumetric  method 
described  above  is  rapid  and,  in  practised  hands,  good,  but  is 
always  a  stumbling  block  to  students.  Messrs  Clowes  and 
Coleman,  in  their  *  Text-book  of  Quantitative  Analysis,'  describe 
a  gravimetric  method  which  the  author  has  found  very  satis- 
factory, and  which  students  will  be  able  to  carry  out  without 
much  difficulty. 

Filter  paper  absorbs  a  certain  amount  of  copper  sulphate 
which  obstinately  refuses  to  be  washed  out.  It  is  therefore 
necessary  to  prepare  an  asbestos  filter,  and  it  is  on  the  prepara- 
tion of  this  filter  that  the  accuracy  of  the  determination  depends. 
A   'calcium    chloride'   tube   of    the    shape    shown    on    the 


84]  Estimation  of  Sugar  55 

apparatus  in  fig.  20  (page  32),  4  or  5  inches  long,  is  carefully 
cleaned  and  a  tightly  fitting  disc  of  platinum  foil  which  has 
been  perforated  is  passed  down  the  wider  end  to  block  up  the 
thinner  tube.  A  little  good  asbestos  is  carefully  torn  up,  then 
reduced  to  a  pulp  with  water,  and  poured  into  the  tube ;  this  is 
pressed  down  carefully,  and  then  a  little  more  pulp  poured  in 
until  a  felted  mass  about  \  inch  thick  has  been  formed  over 
the  platinum.  The  tube  is  then  connected  with  a  filter  pump 
and  washed  successively  with  dilute  sulphuric  acid,  caustic 
potash,  hot  water,  alcohol,  and  finally  ether.  It  is  then  dried 
in  a  steam  oven  and  weighed.  When  this  is  ready  the  estima- 
tion may  be  carried  out  as  follows  : 

'  Thirty  c.c.  of  the  copper  solution  and  30  c.c.  of  the  tartrate 
solution  [paragraph  80]  are  mixed  with  60  c.c.  of  water  in  a 
beaker.  The  liquid  is  heated  by  immersing  the  beaker  in 
boiling  water.  Twenty-five  c.c.  of  the  sugar  solution,  which 
must  not  contain  more  than  0*25  glucose,  are  then  heated  to 
boiling  and  added  to  the  liquid  in  the  beaker,  and  the  beaker 
is  heated  in  the  boiling  water  for  ten  minutes  longer. 

'  The  liquid  is  then  quickly  filtered  through  the  asbestos 
filter,  using  the  filter  pump,  and  the  cuprous  oxide  is  well 
washed  in  the  filter  with  boiling  water,  then  with  alcohol,  and 
finally  with  ether.     It  is  dried  in  the  steam  oven  and  weighed.'  ^ 

The  weight  of  cuprous  oxide  thus  found,  multiplied  by 
0-5045,  equals  the  weight  of  glucose  in  the  solution. 

'  Clowes  and  Coleman. 


[85 


PART    III 

THE  ESTIMATION  OF  NITROGEN 

The  percentage  of  nitrogen  affects  the  value  of  both  feeding 
materials  and  manures  to  a  greater  extent  than  that  of  any 
other  element  The  determination  of  nitrogen  is  conse- 
quently an  operation  of  the  greatest  importance  in  agricultural 
work.  It  has  therefore  been  thought  well  to  devote  a  chapter 
entirely  to  describing  the  best  methods  at  present  in  use  for 
making  this  estimation. 

85.  Permanent  Apparatus. — In  all  agricultural  labora- 
tories apparatus  is  kept  permanently  set  up  for  the  determina- 
tion of  nitrogen.  It  should  be  remembered,  therefore,  that 
although  some  processes — Kjeldahl's,  for  instance — may  seem 
very  long  and  tedious  when  only  one  estimation  is  required, 
they  become  comparatively  simple  when  the  apparatus  is  once 
set  up  and  used  frequently. 

Fig.  25  is  taken  from  a  photograph  of  the  bench  used  for 
nitrogen  determination  in  the  laboratory  of  the  Notts  County 
Council.  The  two  bottles  a  and  b  contain  respectively  standard 
acid  and  alkali  which  may  be  run  into  the  burettes  beneath. 
The  bottle  c  contains  strong  caustic  soda,  and  is  in  connection 
with  an  arrangement  for  measuring  out  100  c.c.  at  a  time.  On 
the  lower  shelf  are  bottles  containing  the  various  substances 
used  in  the  different  processes,  and  on  the  bench  are  different 
pieces  of  apparatus  which  are  dealt  with  in  detail  in  the 
descriptions  of  those  processes  for  which  they  are  used. 


85] 


Estimation  of  Nitrogen 


57 


Other  permanent  apparatus  is  shown  in  figs.  27,  28,  29, 
and  30. 

The  student  should  make  himself  thoroughly  expert  in  those 
forms  of  nitrogen  estimation  described  in  paragraphs  86  to  96 


Fig.  25. 


before  he  proceeds  to  the  analysis  of  feeding  materials.  The  re- 
maining methods^  which  include  the  estimation  of  nitrogen  when 
nitrates  are  present,  may  be  conveniently  left  over  until  the  end  of 


58  The  Estimation  of  Nitrogen  [86, 87 

Part   F.,  Imt  must  be  thoroughly  mastered  before  attempting  the 
analysis  of  manures. 


THE   SODA   LIME   PROCESS   (WILL  AND 
VARRENTRAP) 

86.  Substance  used.— Urea,  CO(NH2)2. 

Method. — The  substance  is  decomposed  by  contact  with 
red-hot  soda  lime,  and  the  ammonia  thus  evolved  absorbed  in 
standard  sulphuric  acid.  The  amount  of  acid  thus  neutralised 
is  determined  by  titration  with  standard  caustic  potash. 

87.  This  determination  may  be  made  in  a  hard  glass  tube 
which  has  been  sealed  at  one  end,  but  as  this  is  very  liable  to 
accidents  an  iron  tube  of  about  ^-inch  internal  diameter  which 
has  one  end  welded  up  is  much  preferable.  In  laboratories 
where  this  method  is  used  a  supply  of  these  iron  tubes,  varying 
in  length  from  14  to  30  inches,  is  kept.  For  this  experiment 
the  following  apparatus  is  necessary  : 

An  18-inch  iron  tube  (i,  fig.  25). 

A  copper  funnel  (2,  fig.  25). 

A  mortar  and  pestle. 

A  spatula. 

A  Will  and  Varrentrap  bulb  (fig.  26). 

Corks  and  cork  borers, 

A  furnace  (fig.  2  7\ 

Also  the  following  substances  : 

Seminormal  sulphuric  acid. 

/N\ 

Quinquinormal  f  —  J  alkali. 

Granulated  soda  lime. 

A  mixture  of  3  parts  sugar  and  4  parts  soda  lime. 

Asbestos. 


88]  The  Soda  Lime  Process  59 

88.  The  Operation. — First  find  a  cork  to  fit  the  iron 
tube.  Bore  a  hole  through  it  large  enough  to  take  the  end  of 
the  Will  and  Varrentrap  bulb  tube.  Fix  it  as  shown  in  fig.  26. 
Now  run  into  the  bulb  20  c.c.  of  the  seminormal  acid  from  a 
burette  (d,  fig.  25)  and  set  it  on  one  side. 

Next  weigh  out  accurately  about  -3  gram  of  pure  dry  urea. 
Place  the  iron  tubes  in  the  staple  fixed  in  the  drawer,  just  as 
the  tube  stands  in  fig.  25. 
By  means  of  the  copper 
funnel  introduce  sufficient 
of  the  soda  lime  and  sugar 
mixture  to  fill  an  inch  at 
the  end  of  the  tube.  Pour 
as   much  granulated   soda 

°  Fjg.  26. 

lime  as  could  be  held  on  a 

penny  into  the  mortar.  Turn  out  the  urea  on  to  this,  and  just 
cover  it  with  finely  powdered  soda  lime.  Then  add  about 
twice  as  much  granulated  soda  lime  as  is  already  in  the 
mortar,  placing  it  first  on  the  watch  glass  and  pouring  it  thence 
into  the  mortar.  This  ensures  that  all  the  urea  shall  be  re- 
moved from  the  glass.  Now  mix  thoroughly  with  the  steel 
spatula,  and  pour  through  the  funnel  into  the  tube.  Rinse 
out  the  mortar  with  fresh  granulated  soda  lime  several  times, 
pouring  the  rinsings  into  the  tube,  stopping  when  it  is  within 
4  inches  of  the  open  end.  Cover  the  soda  lime  with  a  plug 
of  asbestos  which  fills  about  an  inch  of  the  tube  when  gently 
pressed  down  with  a  thick  glass  rod.  Now  close  the  tube 
with  the  cork  through  which  passes  the  tube  of  the  Will  and 
Varrentrap  bulb. 

The  tube  is  now  ready  for  heating,  which  may  conveniently 
be  done  in  a  Bunsen  combustion  furnace,  as  shown  in  fig.  27, 
but  any  tube  furnace  may  be  used.  (A  few  of  the  tiles  have 
here  been  removed  to  show  the  construction  of  the  furnace.) 


6o 


The  Estimation  of  Nitrogen 


[89 


After  placing  the  tube  in  the  furnace,  turn  on  and  Hght  the  two 
taps  nearest  the  open  end.  Gas  will  be  seen  to  bubble  through 
the  bulbs.  As  soon  as  this  ceases  turn  on  the  next  tap.  The 
bubbles  will  start  again.  When  they  have  ceased,  or  nearly  so, 
turn  on  another.  Continue  turning  on  the  taps  in  this  way 
until  the  whole  tube  is  red  hot. 

The  last  few  taps  will,  of  course,  only  heat  the  mixture  of 
soda  lime  and  sugar  which  was  introduced  first  of  all.  This 
gives  off  various  gases  which  expel  the  last  traces  of  ammonia 
from  the  tube. 

When  all  bubbling  has  ceased,  hold  the  tube  firmly  with  a 
pair  of  glass  pliers,  and  carefully  draw  the  bulbs  out.    (The  glass 


Fig. 


tube  will  come  away,  leaving  cork  adhering  to  the  iron  tube.) 
Empty  the  acid  into  a  large  beaker.  Wash  out  the  bulbs 
twice  with  distilled  water,  pouring  the  washings  into  the  beaker 
which  already  contains  the  acid.  Add  a  few  drops  of  methyl 
orange  solution,  and  titrate  with  the  quinquinormal  alkali, 
using  burette  e,  fig.  25. 

89.  Calculation. — Divide  the  number  of  c.c.  of  potash 
run  into  the  acid  by  2*5,  which  gives  the  number  of  c.c.  of  acid 
which  have  been  neutralised  by  it.  Subtract  this  from  20,  and 
you  have  the  number  of  c.c.  of  acid  which  have  been  neutralised 
by  ammonia. 


90]  The  Soda  Lime  Process  6i 

Since  the  sulphuric  acid  solution  is  seminormal,  one  litre 

will  neutralise  -'  grams  of  NH3,  or  one   c.c.   will   neutralise 
2 

-  -Z=:-oo85     gram    of    NH3,    which   is    equivalent    to  — ~ 

=  •007  gram  N.  If,  therefore,  we  multiply  the  number  of 
c.c.  neutralised  by  ammonia  by  '007,  we  obtain  the  weight  of 
N  in  the  urea.  From  this  the  percentage  of  nitrogen  may  be 
calculated. 

THE   SULPHURIC   ACID   METHOD 

This  method  ivas  due  to  Kjeldahl,  but  the  more  accurate 
modification  here  described  is  known  as  Gunning's  process. 

90.  Substance  used. — Since  urea  does  not  require  the 
full  working  of  this  process,  a  sample  of  linseed  cake  whose 
percentage  of  N  is  known  should  be  used. 

Method  employed. — The  substance  is  decomposed  by 
hot  strong  sulphuric  acid,  whose  boiling-point  is  increased  by 
the  addition  of  potassic  sulphate.  The  ammonia  so  formed  is 
expelled  by  means  of  caustic  soda,  and  absorbed  and  estimated 
as  before. 

The  general  principle  of  this  method  was  invented  by 
Kjeldahl,  and  since  the.  time  when  it  was  first  made  public 
a  large  number  of  modifications  have  been  used.  The 
original  method  decomposed  any  organic  matter  by  means  of 
sulphuric  acid,  mercuric  oxide,  and  potassium  permanganate. 
One  writer  recommends  the  use  of  manganese  dioxide  in  place 
of  permanganate.  Others,  again,  have  shown  that  these 
powerful  oxidising  agents  occasionally  oxidise  some  of  the 
nitrogen,  which  thus  escapes  as  an  oxide  of  nitrogen.  The 
method  here  described  is  used  in  some  of  the  principal 
agricultural  laboratories. 


62  The  Estimation  of  Nitrogen  [9i,  92 

91.  Apparatus  required.— This  is  shown  in  figs.  28,  29, 
and  30,  and  described  in  the  text. 

Chemicals  required. — Sulphuric  acid  free  from  nitrogen. 
Strong  caustic  soda  solution.  This  is  prepared  by  dissolving 
357  grams  of  98  per  cent,  caustic  soda  in  the  least  possible 
quantity  of  water  and  making  up  to  a  litre.  It  is  kept  in  the 
arrangement  shown  at  c,  fig.  25.  The  bottle  has  a  soda  lime 
tube  above  to  prevent  the  access  of  CO2.  By  opening  the 
pinchcock,  the  solution  is  allowed  to  run  into  the  tube,  which 
has  two  marks  upon  it.  When  it  is  full  up  to  the  topmost  mark, 
the  cock  is  closed  and  the  liquid  is  run  out  below  into  a  beaker, 
until  the  level  in  the  tube  is  that  of  the  bottom  mark.  This 
measures  out  exactly  100  c.c. 

Anhydrous  potassium  sulphate  is  also  required. 

92.  Heating  with  Acid. — Weigh  out  about  i  gram  of 
linseed  cake,  and  introduce  it  into  an  8-oz.  flask,  taking  care 
that  none  adheres  to  the  neck.  Measure  out  20  c.c.  of  strong 
H2SO4  free  from  nitrogen.  Pour  it  on  to  the  cake,  and  heat 
gradually  up  to  the  boiling-point  of  the  acid.^  A  very  con- 
venient stand  for  this  is  shown  in  fig.  28.  The  stand  itself  is 
made  of  iron,  and  a  piece  of  asbestos  cardboard,  a,  pierced 
with  four  holes,  each  3  inches  diameter,  is  used  as  a  rest  for 
the  flasks.  A  sheet-iron  support,  b,  is  fixed  at  the  back  of  the 
stand,  so  that  the  flasks  whilst  heating  may  be  tilted  as  in  the 
figure  ;  this  prevents  loss  by  spirting.  The  heat  is  supplied 
by  the  four  Argand  burners  c,  c,  c,  c.  The  temperature  ob- 
tained by  this  means  is  quite  sufficient  for  the  purpose,  whilst 
the  strong  illumination  of  the  flask  and  its  contents  supplied  by 
the  bright  flame  is  a  great  advantage  to  the  operator. 

When  the  liquid  has  ceased  frothing  (from  twenty  to  forty 

*  It  need  scarcely  be  mentioned  that  the  heating  of  a  carbonaceous  sub- 
stance with  sulphuric  acid  will  give  off  large  quantities  of  sulphur  dioxide 
This  operation  must  therefore  be  carried  out  in  a  draught  cupboard. 


93] 


The  Sulphuric  Acid  Method 


63 


minutes)  it  will  be  quite  black  and  impervious  to  the  light,  but 
also  quite  free  from  clots  of  carbonaceous  matter.  It  is  now 
necessary  to  clear  the  solution.  Place  the  flask  upright  for 
a  moment,  throw  into  it  about  8  grams  of  dry  powdered 
K2SO4,  and  immediately  return  to  the  inclined  position.  The 
potash  salt  will  very  considerably  raise  the  boiling-point  of  the 
acid,  and  at  this  higher  temperature  the  carbonaceous  matter 
in  solution  is  readily  oxidised,  with  evolution  of  SO2.  As  the 
liquid  becomes  clearer  the  light  of  the  Argand  begins  to  pene- 


FlG.  28. 


trate  it,  illuminating  the  white  fumes  in  the  flask.  This  makes 
the  interior  of  the  flask  appear  first  dark  red,  which  changes 
gradually  to  yellow  and  finally  to  white.  It  is  then  allowed  to 
cool.  In  the  figure  the  flask  f  shows  the  beginning  of  the 
operation,  e  is  clearing,  and  d  is  cooling. 

93.  The  Distillation.— The  whole  of  the  nitrogen  being 
now  in  the  shape  of  sulphate  of  ammonia,  the  next  process 
consists  of  distilling  off  the  ammonia  after  setting  it  free  by 
caustic  soda. 

Fig.  29  shows  a  very  convenient  form  of  apparatus. 


64 


The  Estimation  of  Nitrogen 


[93 


A  is  an  ordinary  half-gallon  oil  can  fitted  with  a  good  cork 
pierced  by  two  holes.  Through  one  hole  passes  the  straight 
tube  K,  which  reaches  to  within  an  inch  of  the  bottom  of  the 
can.  Through  the  other  passes  the  delivery  tube  m.  This 
arrangement  serves  as  a  boiler  for  supplying  steam,  b  is  a 
60-oz.  flask  fitted  with  an  india-rubber  stopper  pierced  by  three 
holes.  The  tube  m  passes  through  one  of  these  down  to  the 
bottom  of  the  flask ;  the  other  two  being  occupied  respectively 


Fig.  29. 

by  the  tap  funnel  s  and  the  trap  t.  This  trap  is  merely  a 
device  for  preventing  caustic  soda  from  being  mechanically 
carried  over  into  the  condenser.  Its  <:onstruction  is  sufficiently 
apparent  from  fig.  30.  ^  c  is  a  condenser  of  the  usual  form,  but 
made  of  metal  instead  of  glass,  the  inner  tube  being  of  block 

'  The  trap  may  be  left  out  if  the  tube  leading  from  the  flask  e  be  con- 
tinued straight  upwards  for  a  foot  or  so  before  it  bends  down  to  dip  into 
the  condenser. 


94,  95]  The  Sulphuric  Acid  Method  65 

tin.  This  substance,  whilst  not  acted  upon  by  ammonia,  is  a 
far  better  conductor  of  heat  than  glass,  so  that  a  1 2-inch  con- 
denser is  perfectly  effective,  d  is 
a  long  test  tube  with  a  hole  blown 
through  its  end  at  b.  It  is  fixed 
to  the  end  of  the  condenser  by  a 
cork,  and  dips  to  within  half-an- 
inch  of  the  bottom  of  the  8-oz.  p^^ 

conical  flask  e. 

94.  When  the  apparatus  is  ready,  proceed  with  the  estimation 
in  the  following  manner : 

{a)  Run  20  c.c.  of  seminormal  sulphuric  acid  from  a  burette 
into  the  flask  e.  Insert  the  test  tube  d  and  fix  on  to  the  con- 
denser, as  in  the  figure. 

{b)  Half  fill  the  can  a  with  water,  and  set  it  to  boil. 

(c)  Pour  about  100  c.c.  of  distilled  water  into  the  large  flask  b. 
Then  pour  into  this  water  the  acid  liquid  in  which  the  linseed 
cake  has  been  decomposed.  Wash  out  the  small  flask  three 
times  with  water,  and  add  the  washings  to  the  liquid  in  b. 

{d)  Replace  all  the  apparatus  as  in  the  figure. 

{e)  Measure  out  100  c.c.  of  the  strong  caustic  soda  solution 
(357  grams  per  litre),  and  run  it  through  the  tap  funnel,  s,  into 
the  flask. 

95.  The  distillation  may  now  be  proceeded  with.  Light 
the  lamp  under  a,  and  turn  on  the  water  through  the  condenser. 
In  a  few  minutes  the  liquid  in  b  will  be  raised  to  the  boiling- 
point.  Allow  the  steam  to  pass  for  twenty-five  minutes,  then 
light  the  rose  burner  g.  Let  the  steam  pass  for  five  minutes 
more,  and  the  distillation  will  be  completed. 

Remove  the  test  tube  d  and  flask  e  from  the  condenser. 
Take  the  tube  from  the  flask,  washing  back  the  adhering  acid. 
Add  a  drop  or  two  of  methyl  orange,  and  titrate  with  standard 
KHO. 

F 


66  The  Estimation  of  Nitrogen  [96-98 

The  calculation  is  exactly  the  same  as  in  the  soda  lime 
process. 

96.  Comparison  of  the  Two  Methods.— The  soda 
lime  process  has  the  advantage  of  requiring  little  or  no  appara- 
tus but  what  may  be  found  in  any  laboratory,  but  it  possesses 
the  disadvantage  that  the  acid  in  the  bulb  is  often  much 
discoloured  during  the  operation,  thus  rendering  accurate 
titration  very  difficult.  Another  disadvantage  which  is  not  at 
all  shared  by  the  acid  process  is  that  the  substance  for  analysis 
must  be  very  finely  divided.  When  such  materials  as  horn  and 
dried  blood  have  to  be  analysed,  fine  grinding  is  next  to  im- 
possible, and  very  erroneous  results  are  often  obtained.  In  all 
cases  where  grinding  is  difficult,  the  substance  should,  be 
ground  finely  enough  to  enable  the  operator  to  weigh  out  a 
good  average  sample,  and  the  nitrogen  estimated  by  the  acid 
method. 


ESTIMATION   OF   NITROGEN   IN   PRESENCE   OF 
NITRATES 

97.  Substance  used. — A  mixture  of  three  parts  starch 
and  one  part  ammonium  nitrate,  NH4NO3. 

Method  employed. — The  substance  is  decomposed  by 
sulphuric  acid  and  salicylic  acid,  the  N2O5  being  reduced  mean- 
while to  ammonia  with  zinc-dust.  The  ammonia  is  separated 
and  estimated  as  before. 

98.  Apparatus. — This  is  exactly  the  same  as  is  used  in 
paragraphs  92-96. 

Chemicals. — Sulphuric  and  salicyHc  acids,  prepared   by 
dissolving  2  grams  of  salicylic  acid  in  30  c.c.  of  sulphuric  acid. 
Mercury. 
Sodium  sulphide  solution,  80  grams  per  litre. 


99]  Nitrogen  in  Presence  of  Nitrates  67 

Strong  caustic  soda  and  standard  acid  and  alkali  as  before 
(paragraphs  87  and  91). 

Zinc-dust. 

99.  The  Operation. — Weigh  out  about  a  gram  of  the 
mixture  of  starch  and  ammonium  nitrate.  Transfer  to  an 
8-oz.  flask  and  moisten  with  the  smallest  possible  quantity  of 
water.  Take  especial  care  that  no  dry  particles  are  left  in  the 
flask ;  for  if  such  particles  should  float  on  the  surface  of  the 
acid  when  it  is  poured  into  the  flask,  HNO3  i^3,y  be  given  off 
and  escape.  Pour  into  the  moistened  substance  30  c.c.  of 
sulphuric  acid  in  which  2  grams  of  salicylic  acid  has  been  dis- 
solved. Heat  on  a  stand  (fig.  28)  or  sand  bath  until  all  froth- 
ing ceases.  Whilst  this  preHminary  heating  is  going  on,  weigh 
out  roughly  2  grams  of  zinc-dust.  As  soon  as  the  frothing 
has  ceased  add  this  zinc-dust,  a  little  at  a  time ;  then  add 
about  10  grams  of  K2SO4  and  heat  until  the  liquid  becomes 
colourless.  If,  in  an  hour,  the  liquid  is  still  black  or  contains 
carbonaceous  matter,  the  clearing  may  be  greatly  assisted  by 
the  addition  of  a  drop  of  mercury. 

When  the  liquid  is  quite  clear,  all  the  nitrogen  contained 
in  the  original  substance  will  be  in  the  form  of  ammonium 
sulphate.  If  the  operation  has  been  managed  satisfactorily 
without  the  aid  of  mercury,  the  ammonia  may  be  driven  off* 
by  150  c.c.  of  strong  caustic  soda,  as  described  in  paragraphs 
93-95.  Should  it  have  been  found  necessary  to  use  mercury, 
it  must  be  removed  from  solution  by  adding  25  c.c.  of  the 
sodium  sulphide  solution  together  with  the  caustic  soda.  The 
reason  for  this  is  that  mercury-ammonium  salts  are  apt  to  be 
formed,  which  are  not  completely  decomposed  by  the  strong 
alkah,  and  hence  some  of  the  ammonia  does  not  find  its  way 
into  the  standard  acid. 


F2 


68  The  Estimation  of  Nitrogen  [loo 


TO   DISTINGUISH    BETWEEN    'NITRIC,'   'AMMO- 
NIACAL'  AND   'ORGANIC   NITROGEN 

loo.  The  value  of  the  nitrogen  in  manures  varies  consider- 
ably according  to  whether  it  is  in  a  soluble  or  an  insoluble  state. 
Hence  it  is  often  of  importance  to  discover  in  what  state  this 
element  occurs.     The  three  most  common  occurrences  are : 

*  Nitric,*  where  it  is  in  direct  combination  with  oxygen,  as 

in  a  nitrate  or  nitro-compound ; 

*  Ammoniacal,'   where  it  is  in  direct   combination   with 

hydrogen  and  may  be  driven  off  as  ammonia  by  a  caustic 
alkaline  solution ; 

*  Organic,'  where  it  is  in  combination  with  some  organic 

material  and  is   not   released  as   ammonia  by   caustic 
alkalis. 

A  convenient  substance  for  practising  on  may  be  prepared 
by  mixing  linseed  cake  with  ammonium  sulphate  and  sodium 
nitrate. 

To  obtain  an  analysis  showing  the  relative  quantities  of  the 
different  forms  of  nitrogen  in  this  mixture,  three  operations 
are  necessary. 

Operation  I. — Weigh  out  -5  gram  of  the  mixture.     Place  it 

in  the  large  flask  shown  in  fig.  29,  add  200  c.c.  of  distilled 

water  and  2  grams  of  calcined  magnesia.     Attach  the  absorp- 

N 
tion  flask  containing  20  c.c.  of  —  sulphuric  acid,  and  distil 

2 

exactly  as  described  in  paragraphs  93-95.     Titrate  the  acid 

with  —  caustic  potash,  and  calculate  the  percentage  of  nitrogen 

which  has  been  liberated  by  the  magnesia.     This  will  give  the 
percentage  of  ammoniacal  nitrogen. 


101-103]  Nitrogen  in  Nitrates  6g 

N.B. — This  is  the  ordinary  method  used  to  determine  the 
amount  of  ammonia  in  ammoniacal  salts. 

Operation  II. — Determine  the  nitrogen  by  means  of  the 
acid  process  (paragraphs  92-95).  The  sulphuric  acid  used,  in 
this  case,  will  drive  off  all  the  'nitric'  nitrogen  in  the  form 
of  HNO3.  Thus  the  percentage  of  ammoniacal  +  organic 
nitrogen  will  be  obtained. 

Operation  III. — Determine  the  total  nitrogen  as  explained 
in  paragraphs  97-99. 

loi.  Calculation. — By  these  three  operations  we  obtain 
three  results.  The  first  gives  the  percentage  of  ammoniacal 
nitrogen.  The  difference  between  the  second  and  the  first  is 
the  percentage  of  organic  nitrogen,  and  the  difference  between 
the  third  and  the  second  is  the  percentage  of  '  nitric '  nitrogen. 

RAPID   METHODS   FOR   THE   DETERMINATION 
OF  NITROGEN   IN   NITRATES 

102.  In  cases  where  nothing  but  the  percentage  of  'nitric' 
nitrogen  is  required,  as  in  alkaline  nitrates,  the  above  method 
would  be  very  long  and  tedious.  Therefore,  three  methods 
are  here  given,  each  of  which  has  its  special  recommendations. 

103.  Ulsch's  Method. — This  method  is  the  most  gener- 
ally applicable,  and  is  of  especial  value  in  the  analysis  of 
alkaline  nitrates,  and  mixed  manures  which  contain  nitrates 
but  not  ammonium  salts. 

Method  employed. — The  nitrate  is  reduced  by  iron  and 
dilute  sulphuric  acid.  Ammonium  sulphate  is  thus  formed. 
The  ammonia  is  driven  off  and  estimated  as  before. 

Substance  used. — Potassium  nitrate,  KNO3.  Weigh  out 
accurately  about  2  grams  of  pure  potassium  nitrate,  and  dissolve 
in  a  little  water.  Introduce  the  solution  into  a  loo-c.c.  flask, 
with  all  the  precautions  used  in  making  up  a  standard  solution. 


70  The  Estimation  of  Nitrogen  [104-106 

Add  distilled  water  to  the  loo-c.c.  mark.  Shake  well.  Mea- 
sure out  25  c.c.  of  this  solution  with  a  pipette  into  an  8-oz. 
flask.  Add  5  grams  of  reduced  iron  and  20  c.c.  of  dilute  sul- 
phuric acid  (one  volume  of  acid  to  three  of  water).  Place  the 
flask  in  an  inclined  position  on  the  stand  (fig.  28)  and  allow 
the  reaction  to  continue  without  heating  until  effervescence 
ceases.  Now  heat  to  boiling  for  six  minutes,  then  allow  to  cool. 
The  nitrogen  is  now  in  the  state  of  sulphate  of  ammonia,  and 
may  be  estimated  as  in  paragraph  100,  operation  I.  Instead  of 
magnesia,  however,  add  20  c.c.  of  caustic  soda  solution  and  two 
or  three  lumps  of  clean  granulated  zinc.  The  calculation  in  this 
case  is  similar  to  the  one  in  paragraph  89 ;  but  it  must  be  re- 
membered that,  whereas  about  2  grams  of  the  potassium  nitrate 
were  weighed  out  and  dissolved,  only  one  quarter  of  this  solu- 
tion was  used. 

104.  Schloesing's  Method  {modified).— This  is  a  very 
rapid  method,  and  is  generally  used  for  the  estimation  of  the 
nitrates  in  soils.  It  may,  however,  be  advantageously  used  in 
the  estimation  of  nitrogen  in  alkaline  nitrates  and  manures. 

Method. — The  nitrate  is  decomposed  by  sulphuric  acid 
and  ferrous  sulphate  according  to  the  equation 

aNaNOa  +  eFeSO^  +  ^n^O^  =  2NO  +  sFe.lSOJg  +  NagSO^  +  4H2O. 

The  nitric  oxide  is  measured. 

105.  Apparatus. — Many  forms  of  apparatus  are  used  for 
this  operation.  Of  the  two  described  here,  the  first  is  in  use 
at  the  laboratory  of  the  Royal  Agricultural  Society  of  England, 
and  has  the  great  advantage  that  no  other  gas  excepting  the 
nitric  oxide  and  a  little  water  vapour  is  present  in  any  part  of 
the  apparatus.  The  second  one  is  more  readily  prepared  but 
less  easily  worked. 

106.  The  first  apparatus  is  shown  in  fig.  31.  a  is  a  round- 
bottomed  flask,  in  which  the  reaction  is  to  take  place,     b  is  a 


107] 


Nitrogen  in  Nitrates 


71 


tap  funnel  by  which  the  liquid  may  be  introduced  into  a.  c  is 
a  trap  joint  which  prevents  any  of  the  solution  from  getting 
into  the  side  tube  d.  The  tube  d,  by  which  the  gas  is  to 
escape,  bends  twice  at  angles  of  135°,  and  is  at  least  36  inches 
in  length  from  the  second  bend,  G,  to  the  lower  outlet.  The 
end  N  is  recurved  into  a  hook,  so  that  the  gas  may  pass  into 
the  measuring  tube,  k,  which  stands  in  a  trough  of  mercury,  f. 


Fig,  31. 

107.  The  Experiment. — Fix  the  tap  funnel  firmly  in  the 
clip  of  a  retort  stand,  in  the  position  shown  in  the  figure,  so 
that  the  side  tube  may  fall  over  the  side  of  the  bench.  Place 
the  mercury  trough  beneath  the  outlet  n.  Fix  the  flask  a  in 
position,  and  the  apparatus  is  ready  for  work. 

Weigh  out  about  i  gram  of  pure  KNO3  and  dissolve  in  a 
loo-c.c.  flask,  as  directed  in  paragraph  103.    Measure  out  20  cc. 


72  The  Estimation  of  Nitrogen  [107 

with  a  pipette  and  run  it  into  the  flask  a,  washing  it  in  with  20  c.c. 
of  warm  water.  Next  weigh  out  roughly  a  gram  of  pure  ferrous 
sulphate  and  dissolve  it  in  20  c.c.  of  hot  water  to  which  a  drop 
of  sulphuric  acid  has  been  added.  Whilst  it  is  dissolving,  close 
the  stopcock  of  the  funnel,  see  that  the  end  of  the  evolution 
tube  dips  under  the  mercury,  and  boil  the  liquid  in  the  flask 
until  it  is  reduced  to  about  half  its  bulk.  This  will  drive  all 
air  out  of  the  apparatus,  and  on  allowing  it  to  cool  the  mer- 
cury will  rise  in  the  side  tube  nearly  to  the  barometric  height. 
If  the  mercury  does  not  rise  freely,  then  there  is  some  leak  in  the 
apparatus.  Should  all  go  well,  heat  up  again  to  boiling  and  pour 
the  ferrous  sulphate  solution  into  b.  Turn  on  the  tap  cautiously, 
and  allow  nearly  all  the  liquid  to  run  into  the  flask.  Now  fill 
the  measuring  tube,  k,  with  mercury,  and  invert  it  over  the  end 
of  the  evolution  tube.  Pour  40  c.c.  of  strong  sulphuric  acid  into 
B,  and  turn  on  the  tap  so  that  the  acid  may  drop  slowly  into 
the  flask.  Nitric  oxide  will  at  once  come  off.  When  nearly  all 
the  acid  has  been  added  (only  so  much  being  left  as  will  pre- 
vent the  access  of  air  to  the  tap),  turn  off  the  tap  and  heat 
the  flask  cautiously.  After  all  the  gas  has  come  off  from  the 
apparatus — />.,  when  it  ceases  to  collect  in  k — boil  briskly  for 
half-a-minute,  and  allow  to  cool.  Remove  the  measuring  tube 
to  the  deepest  part  of  the  trough,  and  allow  to  stand  for  an 
hour  to  cool.  When  cold,  sink  the  tube  until  the  mercury 
stands  at  the  same  level  inside  and  outside.  Now  read  off  the 
volume  of  the  gas.  Usually  a  little  water  collects  over  the 
mercury  inside  the  tube.  In  adjusting  the  levels  of  the  mer- 
cury this  is  neglected,  but  the  volume  of  the  water  must  be 
noted.  Note  also  the  height  of  the  barometer  and  the 
temperature  of  the  air  in  the  room. 

Nitric  oxide  is  slightly  soluble  in  water,  and  therefore  an 
allowance  must  be  made.  Experiment  has  shown  that  under 
the  conditions  of  this  experiment  the  water  which  collects  in 


108]  Nitrogen  in  Nitrates  73 

the  tube  dissolves  one  twentieth  of  its  volume  of  gas.  The 
total  volume  of  gas  evolved  is  therefore  the  volume  read  off  on 
the  collecting  vessel  +  -^^  the  volume  of  water  standing  above 
the  mercury. 

108.  Calculation. — Having  found  the  volume  of  gas, 
including  the  correction  for  solubility,  at  a  certain  known 
temperature  and  pressure,  the  first  thing  to  do  is  to  find  what 
that  volume  would  be  at  the  normal  temperature  and  pressure 
of  0°  C.  and  760  mm.     This  is  done  by  the  formula 


V.  = 


V1X273X/ 


(273  +  0x760 
where  V2=volume  at  0°  C.  and  760  mm.  ; 
Vi=  volume  noted; 
/= pressure  noted  in  millimetres  ; 
/= temperature  noted  in  degrees  Centigrade. 

For  the  explanation  of  this  formula  the  student  is  referred  to  any 
elementary  book  on  physics. 

Having  reduced  our  volume  to  normal  temperature  and 
pressure,  we  make  use  of  the  following  data :  i  c.c.  of  NO  at 
0°  C.  and  760  mm.  represents  i'343  milligram  of  NO.  This  is 
equivalent  to  '627  milligram  of  nitrogen  or  3*805  of  NaNOa.^ 
We  have,  therefore,  only  to  multiply  the  reduced  volume  in 
c.c.  by  -000627  to  find  the  weight  of  N  present  in  the  KNO3, 
and  from  this  we  may  calculate  the  percentage.  When  a  large 
number  of  estimations  have  to  be  made  this  calculation  be- 
comes somewhat  tedious.  The  table  on  pages  74-77  will 
simplify  this  very  much.  This  table  contains  a  set  of  factors 
which  are  used  as  follows  : 

Having  read  off  the  temperature  and  the  pressure,  refer  to 

'  Sodium  nitrate  is  mentioned  here,  as  it  is  the  substance  in  which 
agricultural  analysts  most  commonly  have  to  carry  out  this  estimation. 
Potassium  nitrate  is  suggested  for  the  student,  as  it  is  more  easily  prepared 
in  the  pure  state. 


74 


The  Estimation  of  Nitrogen 


[108 


Table  for  Reducing  Volumes  of  Gas  to  o°  C. 

AND    760  MM. 


730 

7° 

8° 

•9365 

•9332 

731 

•9378 

•9345 

732 

•9391 

•9357 

733 

•9404 

•9370 

734 

•9416 

•9383 

735 

•9429 

•9396 

736 

•9442 

•9408 

737 

•9455 

•9421 

738 

•9468 

•9434 

739 

•9481 

•9447 

740 

•9493 

•9459 

741 

•9506 

•9472 

742 

•9519 

•9485 

743 

•9532 

•9498 

744 

•9545 

•95 1 1 

745 

•9558 

•9523 

746 

•9570 

•9536 

747 

•9583 

•9549 

748 

•9596 

•9562 

749 

-9609 

•9575 
•9587 

750 

•9622 

751 

•9635 

•9600 

752 

•9647 

•9613 

753 

•9660 

•9626 

754 

•9673 

1 

•9638 

•9299 
•93II 
•9324 
•9337 
•9350 
•9362 

•9375 
•9388 
•9401 
•9413 


•9426 
•9439 
•9452 
•9464 

•9477 
•9490 
•9502 
•9515 
•9528 
•9541 


•9266  -9233 

•9278  !  -9246 

•9291  '9258 

•9304  -9271 

•9317  i  -9284 

•9329  !  '9297 

•9342  !  -9309 

•9354  !  ^9321 

•9368  1  -9335 

•9381  j  -9348 


•9393 
•9406 
•9419 
•9431 
•9444 
•9457 
•9469 
•9482 
•9495 
•9507 


•9360 

•9373 
•9386 

•9398 
•941 1 
•9424 
•9436 
•9449 
•9462 

•9474 


•9554  \  -9520  -9486 

•9566  I  -9533  -9499 

•9579  '  ^9545  1  ^95 12 

•9592  -9558  -9524 


•9604   -9571 


•9536 


•9201 
•9214 
•9226 
•9239 
•9252 
•9264 
•9276 
•9288 
•9302 
•9315 

•9327 
•9340 
•9352 
•9365 
•9378 
•9390 

■9403 
•9416 
•9428 
•9441 


•9453 
•9466 
•9478 
•9491 
•9503 


13° 

14° 

•9169 

•9137 

•9182 

•9150 

•9194 

•9162 

•9207 

•9175 

•9220 

•9187 

•9232 

•9200 

•9244 

•9212 

•9255 

•9225 

•9269 

•9237 

•9282 

•9250 

•9294 

•9262 

•9307 

•9275 

•9320 

•9287 1 

•9332 

•9300 

•9345 

•9312 

•9357 

•9325 

•9370 

•9337 

•9383 

•9350 

•9395 

•9362 

•9408 

•9375 

•9421 

•9387 

•9434 

•9400 

•9446 

•9412 

•9459 

•9425  1 

•9471 

•9437 

108] 


Nitrogen  in  Nitrates 


75 


Table  for  Reducing  Volumes  of  Gas  to  o°C. 
AND   760  MM.  {continued). 


— 

15° 

16° 

17° 

18° 

19° 

20° 

21° 

1 

! 
22° 

730 

•9105 

•9074 

•9042 

•901 1 

•8980 

•8950 

•8919 

•8887 

731 

•9118 

•9086 

•9055 

•9023 

•8993 

•8962 

•8932 

•8899 

732 

•9130 

•9099 

•9067 

•9035 

•9005 

•8974 

•8944 

•891 1 

733 

•9143 

•91 1 1 

•9079 

•9048 

•9017 

•8986 

•8956 

•8923  1 

734 

•9155 

•9123 

•9092 

•9060 

•9030 

•8999 

•8968 

•8935 

735 

•9168 

•9136 

•9104 

•9072 

•9042 

•901 1 

•8980 

•8948 

736 

•9180 

•9148 

•9116 

■9085 

•9054 

•9023 

•8993 

•8960 

737 

•9193 

•9161 

•9129 

•9098 

•9067 

•9035 

•9005 

•8972 

738 

•9205 

•9172 

•9141 

•91 10 

•9079 

•9047 

•9017 

•8984 

739 

•92J18 

•9186 

•9153 

•9122 

•9091 

•9059 

•9029 

•8996 

740 

•9230 

•9198 

•9166 

•9135 

•9103 

•9071 

•9041 

•9009 

741 

•9243 

•92 1 1 

•9178 

•9147 

•9116 

•9084 

•9054 

•9021 

742 

'9255 

•9223 

•9191 

•9159 

•9128 

•9096 

•9066 

•9033 

743 

•9268 

•9236 

.9203 

•9172 

•9140 

•9108 

•9078 

•9045 

744 

•9280 

•9248 

•9215 

•9184 

•9153 

•9120 

•9090 

•9057 

745 

•9293 

•9261 

•9228 

•9197 

•9165 

•9133 

•9102 

•9070 

746 

•9305 

•9273 

•9240 

•9209 

•9177 

•9145 

•9115 

•9082 

747 

•9318 

•9285 

•9252 

•9221 

•9190 

•9157 

•9127 

•9094 

748 

•9330 

•9297 

•9265 

•9234 

•9202 

•9169 

•9139 

•9106 

749 

•9343 

•9310 

•9277 

•9246 

•9214 

•9182 

•9151 

•9118 

750 

•9354 

•9322 

•9290 

•9258 

•9226 

•9194 

•9164 

•9^30 

751 

•9367 

•9335 

•9302 

•9270 

•9239 

•9206 

•9176 

•9143 

752 

•9379 

•9347 

•9314 

•9283 

•9251 

•9218 

•9188 

•9155 

753 

•9392 

•9360 

•9327 

•9295 

•9263 

•9231 

•9200 

•9167 

754 

•9404 

•9372 

•9339 

•9307 

•9276 

•9243 

•9212 

•9179 

i 

J6 


Tht  Estimithn    of  Nitrogen 


[108 


Table  for  Reducing  Volumes  of  Gas  to  q°  C. 
AND  760  MM.  {conlintiea). 


— 

r 

8° 

9° 

10° 

11° 

12° 

13° 

14° 

755 

•9686 

•9651 

•9617 

•9583 

•9548 

•9516 

•9484 

•9450 

756 

•9699 

•9664 

•9630 

•9596 

•9561 

•9528 

•9496 

•9462  1 

757 

•9712 

•9677 

•9643 

•9609 

•9574 

•9541 

•9509 

•9475  1 

758 

•9724 

•9690 

•9655 

•9621 

•9587 

•9554 

•9522 

•9487 

759 

•9737 

•9702 

•9668 

•9633 

•9600 

•9566 

•9535 

•9500 

760 

•9750 

•9715 

•9681 

•9646 

•9613 

•9579 

•9547 

•9512 

761 

•9763 

•9728 

•9693 

•9659 

•9625 

•9591 

•9560 

•9525 

762 

•9776 

•9741 

•9706 

•9672 

•9638 

•9604 

•9572 

•9537 

763 

•9788 

•9754 

•9719 

•9684 

•9650 

•9617 

•9585 

•9550 

764 

•9801 

•9766 

•9732 

•9697 

•9663 

•9630 

•9598 

•9562 

765 

•9814 

•9779 

•9744 

•9710 

•9676 

•9642 

•9610 

•9575 

766 

•9827 

•9792 

•9757 

•9722 

•9688 

•9655 

•9623 

•9587 

767 

•9840 

•9805 

•9770 

•9735 

•9701 

•9668 

•9635 

•9600 

768 

•9853 

•9817 

•9783 

•9748 

•9714 

•9680 

•9648 

•9612 

769 
770 

•9865 

•9830 

•9795 

•9760 

•9726 
•9739 

•9693 
•9705 

•9660 

•9625 

•9878 

•9843 

•9808 

•9773 

■9673 

•9637 

771 

•9891 

•9856 

•9821 

•9786 

•9752 

•9718 

•9685 

•9650 

772 

•9904 

•9868 

•9834 

•9798 

•9764 

•9731 

•9698 

•9662 

773 

•9917 

•9881 

•9846 

•981 1 

•9777 

•9743 

•9710 

•9675 

774 

•9930 

•9894 

•9859 

•9824 

•9790 

•9751 

•9723 

•9687 

775 

•9942 

•9907 

•9872 

•9836 

•9802 

•9768 

•9735 

•9700 

776 

•9955 

•9919 

•9884 

•9849 

•9815 

•9781 

•9748 

•9712 

777 

•9968 

•9932 

•9897 

•9862 

•9828 

•9794 

•9760 

•9725 

778 

•9981 

•9945 

•9910 

•9874 

•9840 

•9806 

•9773 

•9737 

779 
780 

•9994 

•9958 

•9923 

•9887 

•9853 

•9819 

•9785 

•9750 
•9762 

1-0007 

•9971 

•9935 

•9899 

•9866 

•9831 

•9798 

108] 


Nitrogen  in  Nitrates 


77 


Table  for  Reducing  Volumes  of  Gas  to  o°  C. 
AND  760  MM.  {continued). 


— 

15° 

16° 

17° 

18° 

19° 

20° 

21° 

22° 

755 

•9417 

•9385 

•9351 

•9320 

•9288 

•9255 

•9225 

•9191 

756 

•9429 

•9397 

•9364 

•9332 

•9300 

•9267 

•9237 

•9204 

757 

•9442 

•9410 

.9376 

•9344 

•9313 

■9280 

•9249 

•9216 

758 

•9454 

•9422 

•9389 

•9357 

•9325 

•9292 

•9261 

•9228 

759 

•9467 

•9434 
•9446 

•9401 

•9369 

•9337 

•9304 

•9273 

•9240 

760 

•9479 

•9414 

•9381 

•9349 

•9316 

•9286 

•9252 

761 

•9492 

•9459 

•9426 

•9394 

•9362 

•9329 

•9298 

•9264 

762 

•9504 

•9471 

•9438 

•9406 

•9374 

•9341 

•9310 

•9276 

763 

•9517 

•9484 

•9451 

•9418 

•9387 

•9353 

•9322 

•9289 

764 

•9529 

•9496 

•9463 

•9431 

•9399 

•9365 

•9334 

•9301 

765 

•9542 

•9509 

•9475 

•9443 

•941 1 

•9378 

•9347 

•9313 

766 

•9554 

•9521 

•9488 

•9455 

•9424 

•9390 

•9359 

•9325 

767 

•9567 

•9533 

9500 

•9468 

•9436 

•9402 

•9371 

•9337 

768 

•9579 

•9545 

•9512 

•9480 

•9448 

•9414 

•9383 

•9349 

769 

•9592 

•9558 

•9525 

•9492 

•9460 

•9427 

•9395 

•9362 

770 

•9604 

•9571 

•9538 

•9505 

•9472 

•9439 

•9408 

•9374 

771 

•9617 

•9583 

•9550 

•9517 

•9485 

•9451 

.9420 

•9386 

772 

•9629 

•9595 

•9562 

•9529 

•9497 

•9463 

•9432 

•9398 

773 

•9642 

•9608 

•9575 

•9542 

•9509 

•9476 

•9444 

•9410 

774 

•9654 

•9620 

•9587 

•9554 

•9522 

•9488 

•9456 

•9422 

775 

•9667 

•9632 

•9600 

•9566 

•9534 

•9500 

•9469 

•9435 

776 

•9679 

•9644 

•9613 

•9579 

•9546 

•9512 

•9481 

•9447 

777 

•9692 

•9657 

•9625 

•9591 

•9559 

•9525 

•9493 

•9459 

778 

•9704 

•9670 

•9638 

•9603 

•9571 

•9537 

•9505 

•9471 

779 

•9717 

•9682 

•9650 
•9662 

•9615 
•9628 

•9582 

•9549 

•9517 

•9483 
.9496 

780 

.9729 

•9695 

•9595 

•9562 

•9530 

78 


The  Estimation  of  Nitrogen 


[109 


the  table ;  find  the  figure  denoting  the  number  of  millimetres 
of  pressure  in  the  first  column,  and  glance  along  this  line  until 
you  come  to  the  column  which  is  headed  by  the  number  of 
degrees  Centigrade  which  you  have  read  off  on  the  thermometer. 
Multiply  the  number  of  c.c.  of  gas  obtained  by  the  factor  here 
found.  The  product  will  be  the  volume  at  o°  C.  and  760  mm. 
For  instance,  supposing  we  found  our  volume  to  be  89.2  c.c. 
at  17°  and  772  mm.,  we  find  the  factor  for  this  temperature 
and  pressure  in  the  table  to  be  '9562.  We  calculate  the  volume 
at  0°  C.  and  760  mm.  thus : 

89-2  X  "9562  =  85-29 

and  multiplying   this  by  "000627  we  get  the  weight  of  N  ^in 
our  substance — i.e.^  *o5348  gram. 

109.   The   second  apparatus   is   shown   in   fig.    32.     The 
operation  is  carried  on  in  the  flask  a,  which  is  of  6-oz.  capacity 


Fig.  32. 


and  is  fitted  with  an  india-rubber  stopper  in  which  two  holes 
have  been  bored.  Through  one  passes  the  tap  funnel  b, 
through  the  other  an  evolution  tube,  c  o,  which  is  cut  at  d  and 
joined  with  a  piece  of  india-rubber,  which  can  be  closed  at  will 


110-112]  Nitrogen  in  Nitrates  79 

by  a   pinchcock.     The   pneumatic   trough,    e,    is   filled   with 
water. 

This  apparatus  is  arranged  specially  for  estimating  the 
amount  of  nitric  nitrogen  in  commercial  nitrate  of  soda,  and 
has  to  be  calibrated  after  each  operation.  The  method  may 
be  briefly  described  as  follows.     Make  up  solutions  of 

I  gram  pure  NaNOg  made  up  to  100  c.c. 

1  gram  commercial  NaNOa  made  up  to  100  c.c. 

2  grams  FeS04  dissolved  in  50  c.c.  of  water  and  a  drop 

of  H2SO4. 

When  passing  a  slightly  soluble  gas  like  nitric  oxide  through 
large  quantities  of  water,  it  is  practically  impossible  to  make 
any  correct  allowance  for  the  quantity  that  may  be  lost.  The 
only  plan,  therefore,  is  to  make  a  comparison  between  the 
volume  of  gas  obtained  from  a  pure  sample  of  the  nitrate  and 
that  obtained  from  the  sample  under  consideration. 

iia  Calibration. — Boil  20  c.c.  of  the  pure  NaNOg  solu- 
tion with  20  c.c.  water  as  before  to  expel  air.  Close  the  india- 
rubber  joint  D  and  add  25  c.c.  FeSO^  solution.  Place  the 
collecting  tube  in  position,  and  add  50  c.c.  strong  sulphuric 
acid  cautiously  to  the  liquid  in  the  flask,  opening  d  at  the  same 
time.  Complete  the  reaction  exactly  as  in  the  other  apparatus. 
Read  off"  the  volume  of  gas. 

111.  The  Hstimation. — Wash  out  the  apparatus  imme- 
diately the  calibration  is  finished,  and  do  a  second  operation, 
using  20  c.c.  of  the  commercial  nitrate  solution. 

112.  Calculation. — This  is  very  simple,  being  a  mere 
comparison  of  the  two  results.  Thus,  supposing  the  calibra- 
tion gave  X  c.c.  of  gas  and  the  estimation  y  c.c,  then  the 
percentage  of  pure  NaNOa  i^  the  commercial  sample  would 

be<-  100.     There  is  no  need,  with  this  apparatus,  to  correct 

X 


8o 


The  Estimation  of  Nitrogen 


[113,  114 


for  temperature  and  pressure,  as  the  two  operations  were  con- 
ducted under  as  nearly  as  possible  the  same  conditions. 

113.  Lunge's  Nitrometer  Method.— Lunge's  nitro- 
meter was  originally  invented  to  estimate  the  amount  of  nitrogen 
in  '  nitrous  vitriol.'  Two  modern  forms  of  the  apparatus  are 
shown  in  figs.  33  and  34,  the  only  difference  between  the 
two  forms  being  their  capacity.  In 
fig.  33  <2  is  a  calibrated  tube  con- 
nected above  with  a  three-way 
tap,  d,  and  below  with  a  piece  of 
stout-walled  india-rubber  tubing  c. 
The  tube  b  is  not  calibrated.    /  is 


Fig.  33. 


Fig.  34. 


a  funnel  by  means  of  which  liquids  may  be  introduced  into 
«,  and  ^  is  a  thick-walled  tube  of  small  bore  by  means  of  which 
gases  may  be  introduced  or  drawn  off.  In  fig.  34  the  same 
parts  are  shown,  but  two  large  bulbs  are  blown  in  the  tubes,  so 
that  the  amount  of  gas  which  may  be  experimented  with  is 
greatly  increased. 

114.  The  Estimation. — Fill  the  apparatus  with  the  bulbs 
(fig.  34)  with  mercury  as  shown  in  fig.  33,  and  turn  the  tap  so  that 


114]  Nitrogen  in  Nitrates  8 1 

communication  is  made  between  the  calibrated  tube  and  the 
air.  Raise  the  tube  b  until  the  mercury  entirely  fills  a.  Close 
the  tap.  Return  b  to  its  position,  clamping  the  tubes  in  a  retort 
stand  as  shown  in  fig.  33.  Weigh  out  about  "3  gram  of  sodium 
nitrate,  and  introduce  the  powder  into  the  funnel.  Add  about 
I  c.c.  of  water.  As  soon  as  the  nitrate  is  dissolved,  draw  it 
into  the  measuring  tube.  Wash  the  cup  with  another  c.c.  of 
water,  and  draw  that  into  the  measuring  tube.  Finally,  add 
15  c.c.  of  pure  strong  sulphuric  acid,  and  draw  that  in. 

Now  unclamp  the  tube  containing  the  acid  mixture,  and 
incline  it  once  or  twice  so  as  to  place  the  mercury  in  contact 
with  the  liquid  ;  gas  will  commence  to  come  off  and  collect  at 
the  top.  When  this  ceases  shake  more  violently,  so  that  the  mer- 
cury at  the  surface  of  contact  gets  broken  up  into  a  number  of 
globules,  thus  coming  into  thorough  contact  with  the  nitric  acid. 
By  this  means  the  whole  of  the  nitrogen  will  be  transformed 
into  nitric  oxide,  and  if  the  tubes  be  clamped  so  that  the  mer- 
cury stands  at  the  same  level  in  both  tubes,'  the  volume  may 
be  read  off.  It  may  be  assumed,  for  measuring  purposes,  that 
mercury  has  6*5  times  the  specific  gravity  of  sulphuric  acid. 
This  must  be  allowed  for  in  adjusting  the  heights  of  the 
columns  in  the  two  tubes.  Allow  the  whole  apparatus  to  cool 
down  for  half-an-hour.  Readjust  the  height  of  the  mercury 
column.  Note  volume  of  gas,  temperature  of  air,  and  height 
of  barometer  in  millimetres. 

The  calculation  is  exactly  the  same  as  that  used  for  Schloe- 
sing's  apparatus  (see  paragraph  108). 


[116,  116 


PART    IV 
SAMPLES  AND  SAMPLING 

115.  Large  quantities  of  material  are  often  valued  by  the 
analysis  of  a  couple  of  grams,  or  even  less,  which  has  been 
taken  from  the  bulk.  Whether  that  analysis  represents  accu- 
rately the  composition  of  the  whole  quantity  or  not  depends, 
therefore,  quite  as  much  upon  the  care  with  which  that  two 
grams  has  been  selected  as  upon  the  accuracy  with  which  the 
analysis  has  been  made.  In  fact,  in  every  case  where  a  sample 
has  been  drawn  from  a  large  bulk  of  material,  there  is  a  certain 
chance  of  error.  The  object  of  careful  and  scientific  sampling 
is  to  reduce  this  chance  to  a  minimum. 

In  practice  all  substances  for  analysis  are  sampled  twice : 
first,  when  the  sample  is  taken  from  the  bulk,  and,  second, 
when  the  analyst  selects  from  this  first  sample  the  portion  upon 
which  he  intends  to  experiment. 

As  a  rule  this  first  operation  is  performed  by  the  person 
who  wishes  to  have  the  analysis  made,  whilst  the  second  is 
done  by  the  analyst.  It  would  seem,  therefore,  at  first  sight 
that  the  second  was  the  only  one  with  which  the  analyst  need 
be  familiar ;  but  the  buyer  or  seller  who  wishes  the  sample  to  be 
analysed  has  often  no  one  to  guide  him  in  the  sampling  except 
the  analyst  himself.  Both  operations  are  described  in  detail 
in  this  chapter.  . 

116,  The  Sampling  of  Minerals.— The  only  cases  in 
which  the  sampling  of  minerals  concerns  the  agricultural  analyst 


117]  Sampling  of  Minerals  83 

are  those  of  mineral  phosphates  and  limestones.  Much  ingenuity 
has  been  expended  in  devising  machinery  and  implements  with 
which  an  accurate  sample  can  be  drawn.  The  simplest  of 
these  is  the  sampling  spade,  shown  in  fig.  35.  When  this  is 
driven  into  a  mass  of  ore  a  certain  small 
quantity  is  collected  in  the  central  com- 
partment, whilst  a  much  larger  portion 
finds  its  place  on  the  sides.  A  dex- 
terous throw  with  the  shovel  sends  all 
the  larger  portion  off  on  to  another  heap, 
leaving  the  small  part  still  in  its  place.  This  is  then  thrown 
on  to  another  spot.  Thus,  after  digging  away  a  large  portion 
from  different  parts  of  the  bulk  we  get  a  large  and  a  small 
heap,  the  small  one  being  a  fair  sample  of  all  the  rest.  By 
repeating  the  operation  on  this  sample  a  still  smaller  sample 
is  obtained. 

When,  by  repeated  samplings  of  this  kind,  a  sufficiently 
small  heap  has  been  formed,  it  is  spread  out  on  the  ground, 
the  larger  lumps  broken  up,  and  half-a-dozen  small  spadefuls 
taken  from  different  parts.  This  small  quantity  is  broken  up 
to  pieces  about  the  size  of  marbles,  spread  out,  and  five  or 
six  handfuls  taken  from  different  parts.  This  portion  may  be 
sent  to  the  laboratory. 

Should  a  sampling  shovel  not  be  available,  the  first  heap 
may  be  made  by  selecting  a  spadeful  at  a  time  from  different 
parts  of  the  bulk,  and  reducing  this  to  smaller  heaps  as  before. 

117.  In  a  sampling  machine  the  whole  mass  of  the  mineral 
is  made  to  pass  through  a  spout  which  is  continually  moving 
backwards  and  forwards  so  as  to  distribute  the  ore  all  over  a 
large  platform.  At  one  part  of  the  platform  is  a  hole,  so  that 
whenever  the  spout  passes  that  place  a  small  portion  of  the 
mineral  falls  through  into  a  receptacle  beneath.  This  portion 
is  again   passed   through   the   machine,  until   it  becomes  of 

G  2 


84  Samples  and  Sampling  [ii8,  119 

workable   size.     It   is   then   broken   up,    and   the   laboratory 
sample  taken  as  before. 

118.  Sampling  aided  by  Grinding.— Fortunately,  in 
agricultural  work,  such  rough  methods  as  those  described  in 
the  last  article  are  seldom  necessary.  The  manure  manufac- 
turer materially  aids  the  sampler  when  he  grinds  the  mineral ; 
for,  whether  it  be  for  the  preparation  of  superphosphate  or  for 
direct  application  to  the  land,  the  substance  must  pass  through 
this  process. 

When  a  mineral  is  ground  or  crushed  two  ends  are  gained. 
In  the  first  place,  the  particles  of  the  substance  are  reduced  in 
size  ;  and,  in  the  second,  these  particles  are  more  or  less 
thoroughly  mixed,  so  that  after  grinding  it  is  far  more  homo- 
geneous in  character  than  it  was  before. 

119.  The  Sampling  of  Manures.— This  subject  has 
been  so  thoroughly  dealt  with  by  Dr.  J.  A.  Voelcker  in 
the  '  Journal  of  the  Royal  Agricultural  Society '  that  no 
better  advice  can  be  given  than  is  contained  in  the  following 
quotation  : 

'  If  a  purchase  consists  of  six  or  any  lesser  number  of  bags, 
each  one  should  be  opened  and  a  portion  drawn  from  each 
bag ;  if  it  consist  of  a  much  larger  number,  then  a  dozen  bags, 
or  certainly  not  less  than  six  bags,  should  be  taken  out  from 
different  parts  of  the  delivery  and  be  set  aside  for  the  purpose 
of  drawing  a  sample  from  them.  Having  set  these  aside,  the 
very  best  way  with  any  ordinary  artificial  manure — such  as 
superphosphate,  dissolved  bones,  bone-meal,  compound 
manures,  nitrate  of  soda,  kainit,  and  other  salts  (anything,  in 
fact,  that  is  in  a  fairly  powdery  and  uniform  condition,  and  not 
bulky  or  matted  together  like  shoddy  or  similar  refuse  mate- 
rials)— is  to  provide  oneself  with  a  special  instrument  which  we 
call  a  "  sampler."  This  is  an  iron  tool  about  2  feet  6  inches 
long,  very  like  a  cheese  sampler,  and  fitted  with  a   wooden 


119]  Sampling  of  Manures  85 

handle.  It  is  made  of  U-shaped  iron,  with  the  end  sharpened 
and  the  edges  rounded;  the  diameter  of  the  groove  being 
about  I  inch.' 

This  is  represented  in  fig.  36. 


1 


Fig.  36. 

'  An  instrument  Uke  this  can  be  driven  down  into  each  of 
the  selected  bags  from  top  to  bottom,  and  by  tilting  the  bag, 
giving  the  sampler  a  twist  round,  and  then  withdrawing  it,  a 
section  of  the  entire  contents  of  the  bag  can  be  obtained. 
This  may  be  repeated  once  or  twice  for  each  bag,  and  other 
similar  sections  taken  from  the  other  bags.  The  different  lots 
withdrawn  must  be  thoroughly  mixed  together.  Any  lump 
should  be  broken  down  with  a  shovel^  and  if  the  heap  is  too 
much  to  form  a  conveniently  sized  sample  for  sending  for 
analysis,  it  should  be  reduced  in  amount  by  division  and  sub- 
division. 

'  This  is  best  done  by  turning  over  the  heap  and  mixing  it 
up  carefully  though  quickly,  flattening  down  any  lumps,  and 
then  dividing  the  heap  into  two  halves ;  one  half  may  be  re- 
jected altogether,  and  the  remainder  again  quickly  turned  over 
and  mixed  thoroughly,  divided  as  before,  and  so  on  as  often  as 
may  be  necessary,  until  a  quantity  weighing  only  three  or  four 
pounds  is  left. 

'  Two  well-fitting  tins,  each  capable  of  holding  from  \  lb. 
to  I  lb.  of  the  material,  should  be  then  filled  from  the  heap 
thus  left.  One  of  these  should  be  wrapped  up  and  sent  by 
post  to  the  analyst,  and  the  other  be  kept  by  the  farmer  for 
reference.  Instead  of  a  tin  a  wide-mouthed  bottle  with  a 
well-fitting  cork  may  be  used,  and  this  be  enclosed  in  a  wooden 


86  Samples  and  Sampling  [119 

box,  and  so  be  sent  by  post  or  rail ;  or  the  sample  may  be 
wrapped  in  tinfoil  or  in  oiled  silk,  and  be  enclosed  in  a  box  or 
in  a  stout  linen  lined  envelope.  This  latter  is  a  very  conve- 
nient form  for  nitrate  of  soda,  sulphate  of  ammonia,  kainit,  and 
similar  salts.  The  tin  is,  on  the  whole,  the  most  satisfactory, 
as  it  is  easy  to  send  from  \  lb.  to  i  lb.  of  manure  in  it,  whilst 
if  a  bottle  or  tinfoil  or  oiled  silk  be  used  it  is  not  easy  to  send 
so  large  a  quantity.  If  a  smaller  quantity  be  sent,  the  heap 
must  be  mixed  still  more  carefully,  and  the  sample  be  taken 
from  different  portions  of  it.  In  no  case,  however,  should  less 
than  4  oz.  be  sent  as  a  sample,  and  when  the  material  is  at  all 
uneven  in  character,  or  lumpy,  or  of  a  mixed  nature,  it  is  not 
satisfactory  unless  a  i-lb.  sample,  or  in  some  cases  as  much  as 
2  lbs.,  be  sent.  The  more  uneven  the  manure,  the  larger  the 
sample  must  be  ;  the  finer  and  more  even  it  is,  the  smaller 
may  be  the  quantity  sent  for  analysis. 

'  One  caution  further  is  necessary.  Whilst  care  must  be 
taken  to  ensure  a  fair  example  being  drawn,  care  must  also  be 
exercised  not  to  let  the  portion  that  is  being  sampled  lie  about 
exposed  too  long.  The  sampling  must  be  done  carefully  but 
also  quickly,  or  the  material  may  dry  considerably  during  the 
process. 

*  In  the  absence  of  a  special  sampling  tool,  such  as  that 
described,  the  best  way  is,  after  selecting  several  bags  as 
directed,  either  to  turn  them  out  one  after  the  other  upon  a 
floor,  and,  taking  a  few  shovelfuls  from  each,  to  mix  these 
shovelfuls  well  together  for  one  sample,  or  (which  is  not  so 
good)  to  drive  a  spade  into  each  of  the  selected  bags  and, 
after  a  little  mixing,  to  draw  out  from  as  near  the  centre  as 
possible  a  couple  of  spadefuls  from  each  bag,  subsequently 
mixing  these  lots  together,  flattening  the  lumps  down,  and 
dividing  and  subdividing  the  heap  until  only  three  or  four 
pounds  are  left.     From  this  the  tins  and  bottles  may  be  filled 


120-122]  Sampling  of  Manures  87 

as  mentioned  before,  one  sample  being  sent  for  analysis  and 
the  other  retained  for  reference.' 

120.  The  sampling  oi  feeding  meal  2ind.  grain  is  conducted 
in  exactly  the  same  manner  as  that  of  manures. 

121.  The  Sampling  of  Oil  Cakes.— Very  frequently  a 
farmer  will  break  a  small  piece  off  the  corner  of  an  oil  cake 
and  send  it  for  analysis. "  This  is  pretty  sure  to  lead  to  an 
erroneous  result.  It  is  well  known  that  the  percentage  of  oil 
varies  considerably  in  different  parts  of  a  cake.  Again,  the 
cakes  may  vary  considerably  one  from  another.  Dr.  Voelcker, 
in  the  article  already  quoted,  recommends  the  following  pro- 
cedure : 

'  A  purchaser  should  first  look  over  the  cakes  comprising 
the  delivery,  and  note  any  difference  of  appearance  that  may 
strike  him,  or  see  whether  all  the  cakes  seem  much  alike.  He 
should  then  select  samples  from  each  different  variety  he 
notices,  the  number  of  samples  being  in  proportion  to  the 
number  of  cakes  of  each  kind  that  make  up  the  bulk.  Three 
or  four  cakes  of  each  sort  should  be  selected,  or,  if  uniform 
throughout,  say  six  cakes  from  the  whole  lot ;  pieces  should 
be  broken  out  of  the  middle,  and  these  pieces  passed  through 
a  cake-breaker.  The  broken  nuts  or  lumps  must  next  be 
mixed  up  thoroughly  and  then  divided  successively,  just  as  was 
advised  in  the  case  of  manures,  until  only  a  couple  of  pounds 
weight  are  left.  Two  tins  may  now  be  filled  with  the  cake, 
one  for  sending  to  the  analyst,  the  other  to  be  kept  for 
reference.' 

By  the  sentence  'Pieces  should  be  broken  out  of  the 
middle '  is  meant  *  Break  a  whole  cake  across  the  middle  ;  then 
off  each  of  the  halves  take  a  strip  about  4  inches  wide,  also 
right  across  the  cake,  and  from  what  was  before  the  middle 
piece  of  the  whole  cake.' 

122.  The  Sampling  of  Hay  Silage,  &c.— When  a  stack 


88  Samples  and  Sampling  [123-125 

is  to  be  valued  by  an  expert,  the  usual  method  of  examination  is 
to  cut  out  a  groove  about  2  feet  wide  by  2  feet  deep,  extending 
from  the  top  to  the  bottom  of  the  stack.  This  is  to  enable 
the  valuer  to  see  the  hay  in  the  interior.  When  this  has  been 
done,  a  sample  for  analysis  may  be  obtained  by  pulling  out 
portions  of  the  freshly  exposed  hay  from  dififerent  levels. 

Another  and,  where  practicable,  better  method  is  to  take 
the  sample  from  different  parts  of  the  stack  whilst  it  is  being 
made.  In  either  case,  the  hay  should  be  cut  up  in  a  clean 
chaff-cutter,  and  placed  in  large  wide-mouthed  bottles  imme- 
diately, so  that  it  may  not  get  damp  or  mouldy,  or,  on  the 
other  hand,  lose  moisture  by  being  stored  in  a  hot  place. 

123.  Water  Samples. — A  sample  of  water  should  be 
taken  in  a  clean  glass-stoppered  Winchester  quart  bottle.  The 
bottle  should  be  washed  out  with  the  water  which  is  to  be 
analysed  before  the  sample  is  taken.  If  it  be  from  a  tap,  the 
water  should  be  allowed  to  run  for  several  minutes  before 
filling  the  bottle.  If  it  be  from  a  well,  the  mouth  of  the 
bottle  should  be  sunk  some  inches  beneath  the  surface  when 
filling. 

For  an  analysis  such  as  is  described  in  this  book,  one 
Winchester  quart  is  sufficient  ;  but  should  a  complete  analysis 
according  to  the  '  Frankland  '  method  be  required,  twice  as 
much  will  be  necessary. 

124.  The  Sampling  of  Soils. — Two  methods  are  in 
vogue  for  the  taking  of  soil  samples.  The  Royal  Agricultural 
Society  recommend  one,  and  the  Highland  and  Agricultural 
Society  another. 

125.  Royal  Agricultural  Society. — 'Have  a  wooden  box 
made  6  inches  long  and  wide,  and  from  9  to  12  inches  deep 
according  to  the  depth  of  soil  and  subsoil  of  the  field.  Mark 
out  in  the  field  a  space  of  about  1 2  inches  square  ;  dig  round, 
in  a  slanting  direction,  a  trench,  so  as  to  leave  undisturbed  a 


126,  127]  Sampling  of  Soils  89 

block  of  soil  with  its  subsoil  from  9  to  12  inches  deep  ;  trim 
this  block  or  plan  of  the  field  so  as  to  make  it  fit  into  the 
wooden  box ;  invert  the  box  over  it,  press  down  firmly,  then 
pass  a  spade  under  the  box  and  lift  it  up.  Gently  turn  over 
the  box  and  nail  on  the  lid.  The  soil  will  then  be  received  in 
the  exact  position  in  which  it  is  found  in  the  field. 

'  In  the  case  of  very  light,  sandy,  and  porous  soils,  the 
wooden  box  may  be  at  once  inverted  over  the  soil,  forced 
down  by  pressure,  and  then  dug  out.' 

126.  Highland  and  Agricultural  Society. — '  Dig  a  little  trench 
about  2  feet  deep,  exposing  the  soil  and  subsoil.  Cut  from  the 
side  of  this  trench  horizontal  scrapings  of  the  soil  down  to  the 
top  of  the  subsoil.  Catch  these  on  a  clean  board,  and  collect 
in  this  manner  about  one  pound  weight  of  soil  taken  from  the 
whole  surface  of  the  section.  Similar  scrapings  of  subsoil 
immediately  below  should  be  taken  and  preserved  separately. 

'  Five  or  six  similarly  drawn  samples  should  be  taken  from 
different  parts  of  the  field,  and  kept  separate  while  being  sent 
to  the  chemist,  that  he  may  examine  them  individually  before 
mixing  in  the  laboratory.' 

127.  Transit. — Where  samples  are  to  be  sent  by  post, 
the  following  precautions  should  be  taken  : 

Bottles  should  be  enclosed  in  boxes  or  hampers. 

Acid  manures  or  ensilage  should  not  be  sent  in  tins,  but  in 
pots  or  bottles. 

Substances  which  are  liable  to  gain  or  lose  moisture  should 
not  be  sent  in  bags,  but  in  closed  tins  or  well-stoppered  jars  or 
bottles. 


90  Samples  and  Sampling  [i  28-131 

PREPARATION   IN   THE   LABORATORY 

1 28.  For  preparing  the  samples  for  analysis,  the  following 
equipment  is  necessary  : 

A  large  iron  mortar  and  pestle.  The  mortar  should  be 
about  12  inches  in  diameter. 

A  steel  spatula,  having  a  blade  10  inches  long  by  i^  inch 
broad.  An  ordinary  butcher's  broad-bladed  knife  will  do 
excellently. 

A  set  of  sieves  having  meshes  varying  from  4  to  16  per  linear 
inch.  Sieves  made  with  wire  gauze  are  often  very  difficult  to 
clean,  which  leads  to  much  waste  of  time.  Perforated  zinc  is 
much  preferable,  and  may  be  obtained  with  different  sized 
holes. 

Some  form  of  mill.  A  coffee-mill  will  do  very  well,  if 
arranged  so  that  it  may  be  taken  to  pieces ;  otherwise  it  will  be 
found  impossible  to  clean  it  thoroughly. 

A  number  of  sheets  of  brown  paper. 

129.  The  preparation  in  the  laboratory  sampling  room, 
varies  according  to  the  texture  of  the  sample.  The  substances 
ordinarily  occurring  may  be  classed  under  the  following  heads : 

130.  Liquids. — Water,  milk,  sewage,  phosphoric  acid,  &c. 
These  need  no  preparation,  as  they  may  be  shaken  up  and 
analysed  at  once. 

131.  Hard  Minerals. —Limestone  and  mineral  phos- 
phates. Break  up  in  an  iron  mortar  until  the  whole  of  the 
sample  may  be  passed  through  a  sieve  with  J-inch  meshes. 
Spread  it  out  on  a  piece  of  brown  paper,  and  select  from  diffe- 
rent parts  of  the  heap  sufficient  to  fill  a  sample  bottle  (lo-oz. 
wide-mouthed  bottles  of  common  glass  are  best).  A  finer 
sample  must  be  prepared  by  selecting  in  the  same  way  about 
20  grams,  and  grinding  up  in  an  agate  mortar  until  the  whole 
will  pass  through  a  sieve  having  90  meshes  to  the  linear  inch. 


132-135]  Preparation  in  the  Laboratory  91 

132.  Soils. — Soils  must  be  first  dried  at  60°  to  70°  C, 
then  sifted  through  a  J-inch  sieve.  The  stones  which  will  not 
pass  the  sieve  are  rejected,  and  the  rest  treated  exactly  like  a 
mineral. 

133.  Moist  Substances.— Superphosphates,  dissolved 
bones,  and  acid  manures.  These  are  the  most  difficult  of  all  to 
obtain  in  a  fine  state.  They  should  be  sifted,  and  the  larger 
pieces  broken  up  by  gently  rolling  round  in  an  iron  mortar. 
Just  before  weighing  out  in  the  laboratory  they  should  be 
pounded  into  a  homogeneous  paste  in  a  small  iron  mortar. 

134.  Soft  Substances.— Wool  waste,  shoddy,  &c.  Must 
be  cut  up  small  with  scissors. 

135.  Cakes. — May  be  broken  into  pieces,  a  fair  sample 
of  the  pieces  selected,  and  ground  fine  in  the  mill. 


[136-138 


PART   V 
ANALYSIS   OF  FEEDING  MATERIALS 

THE   ANALYSIS   OF   OIL   CAKES 

136.  The  examination  of  an  oil  cake  may  be  divided  into 
two  distinct  parts  :  the  quantitative  and  the  qualitative.  These 
will  be  treated  separately,  as  the  first  refers  entirely  to  its  feed- 
ing qualities  and  the  second  to  the  purity  and  wholesomeness 
of  the  seeds  which  it  contains. 

Quantitative   Analysis 

The  substances  usually  estimated  in  a  cake  are  moisture^ 
oily  albuminoids,  woody  fibre,  ash,  and  sand.  To  these  may 
be  added  the  carbohydrates,  which  are  as  a  rule  determined 
by  difference. 

137.  Moisture. — Two  grams  of  the  ground  sample  of 
cake  are  weighed  out  in  a  porcelain  capsule,  and  heated  in 
a  steam  oven  until  of  constant  weight.  Five  hours  is  generally 
sufficient  time  for  this. 

138.  Ash. — The  portion  used  for  the  estimation  of 
moisture  is  removed  to  a  weighed  platinum  dish — sweeping  in 
the  last  traces  with  a  camel's-hair  brush — and  ignited,  until  the 
weight  is  again  constant.  It  must  be  remembered  in  perform- 
ing this  operation  that  some  seeds,  of  which  these  cakes  often 
contain  large  quantities,  have  a  high  percentage  of  alkalis,  and 


.39,  140]        Quantitative  Analysis  of  Oil  Cakes 


93 


the  ash  is  therefore  hable  to  fuse.  Should  this  take  place 
before  all  the  carbonaceous  matter  has  been  burned  off,  the 
liquid  alkali  will  completely  shut  off  the  oxygen  of  the  air  by 
coating  the  particles  of  charred  substance.  As  a  rule,  an 
Argand  burner  with  the  flame  turned  down  low  will  be  found 
to  burn  the  cake  without  any  difficulty ;  but  the  operation 
must  be  watched  carefully,  especially  if  the  cake  in  question 
contain  cotton  seed.  Decorticated  cotton  cakes  give  a  very 
fusible  ash.  Linseed  cakes  need  no  such  precaution,  and  may 
be  ignited  at  a  dull  red  heat.  The  residue  is  cooled  and 
weighed.     It  should  be  quite  white. 

139.  Sand* — Wash  the  ash  out  of  the  platinum  dish 
with  a  jet  of  dilute  HCl  into  a  4-oz.  beaker.  Add  10  c.c.  of 
strong  HCl,  digest  on  the  water  bath  for  ten  minutes,  filter,  and 
wash  well  with  hot  water.  Transfer  the  filter  without  drying  to 
a  platinum  dish.  Heat  up  very  slowly  over  an  Argand.  When 
perfectly  dry,  turn  the  light 
up  strongly  and  ignite  until 
the  paper  is  thoroughly 
burned.     Cool  and  weigh. 

140.  Oil. — The  oil  is 
dissolved  out  from  a 
weighed  quantity  of  the 
cake  by  means  of  ether  and 
weighed  after  drying.  This 
is  done  by  means  of  some 
form  of  Soxhlet's  fat  ex- 
tractor. Fig.  37  shows  three 
of  these,  the  first  of  the 

three  being  the  most  convenient.  The  substance  to  be  ex 
tracted  is  wrapped  in  filter  paper  and  placed  in  the  wide 
tube,  E.  Ether  is  poured  upon  this  until  it  rises  to  the  level 
of  the  top  of  the  bent  syphon  tube,  s.      It  then  runs  along 


Fig.  37. 


94 


Analysis  of  Feeding  Materials 


[140 


this  tube,  and  e  is  thus  completely  [emptied  of  liquid,  A 
convenient  receptacle  is  affixed  to  n,  in  which  the  liquid  may 
be  heated  and  the  ether  vaporised.  The  vapour  passes  up 
the  tube  /,  and  after  being  condensed  in  a  condenser  above, 
falls  back  upon  the  substance  until  the  level  of  the  syphon 
top  is  again  reached,  when  the  operation  will  repeat  auto- 
matically. The  other  extractors  figured  are  exactly  the  same 
in  principle,  but  slightly  different  in  construction. 


Fig.  38. 

The  apparatus,  fully  fitted  up,  is  shown  in  fig.  38. 

The  Soxhlet  extractor,  s,  is  fitted  at  the  top  to  a  condenser, 
c,  and  below  to  a  small  round  flask,  f.  The  corks  a,  a  are 
carefully  selected  for  their  soundness,  and  extracted  with  ether. 
The  flask  f  just  dips  beneath  the  surface  of  the  water  in  the 
bath  A.     For  this  bath  any   tin   of  convenient  size  may  be 


i4ij  Quantitative  Analysis  of  Oil  Cakes  95 

used.  The  water  in  the  bath  is  warmed  to  about  60'  C,  and  kept 
at  that  temperature  by  bubbling  steam  into  it.  A  very  conve- 
nient and  substantial  steam  generator  is  shown  in  fig.  38.  It  is 
made  by  fitting  a  half-gallon  oil  can  with  a  cork,  through  which 
pass  two  tubes — one,  d,  to  conduct  steam  to  the  bath,  and  the 
other,  E,  to  act  as  a  sort  of  safety  tube  and  prevent  the  water 
rushing  back  up  d  when  the  boiler  is  cooled,  e  should  pass 
right  down  to  within  an  inch  of  the  bottom  of  the  oil  can, 
and  stand  out  at  least  six  inches  above  the  cork,  d  should 
terminate  at  one  end  just  inside  the  cork,  whilst  to  the  other 
end  a  metal  T  piece  should  be  attached  to  make  the  distri- 
bution of  steam  more  even. 

141.  The  Operation. — Cut  up  a  sheet  of  white  English 
filter  paper  into  pieces  5  by  8  inches  in  size,  roll  them  into  a 
loose  roll,  and  wash  them  two  or  three  times  with  ether  to 
extract  any  traces  of  fat  which  they  may  contain.  When  dry, 
fold  one  of  these  round  a  piece  of  glass  tubing  of  such  size  that 
the  roll  will  easily  slide  into  the  extractor  (see  fig.  37).  Partially 
withdraw  the  glass  tube  until  about  an  inch  of  the  paper 
roll  projects  beyond  its  end.  Fold  this  projecting  part  of 
paper  so  as  completely  to  block  the  end  of  the  roll  ;  then 
withdraw  the  tube  altogether.  A  sort  of  cartridge  case  will 
thus  be  formed  into  which  the  powdered  cake  may  be  intro- 
duced. 

Weigh  out  about  3  grams  oi finely  ground  cake  on  a  watch 
glass,  and  sweep  it  with  a  camel's-hair  brush  into  the  cartridge 
case. 

Place  the  case  in  the  broad  tube  of  the  extractor,  and  affix 
the  flask  f.  Pour  ether  (S.G.  720)  on  to  the  cake  until  it 
begins  to  syphon  over.  Allow  it  all  to  run  into  the  flask,  then 
half-fill  again.  Fix  the  apparatus  on  to  the  condenser. 
Place  the  water  bath  as  in  the  figure,  and  half-fill  it  with  water 
at  60°  C.    Light  the  lamp  under  b,  and  allow  the  extraction  to 


g6  Analysis  of  Feeding  Materials  [i42 

proceed  until  the  ether  has  passed  over  ten  times.  This  should 
take  one  and  a-half  hour. 

The  extracted  fat  has  now  to  be  weighed.  This  is  sometimes 
done  in  the  extraction  flask,  but  such  a  proceeding  is  not  ad- 
visable, as  the  oil  takes  a  much  longer  time  to  dry  in  a  flask 
than  in  a  more  open  vessel. 

Whilst  the  extraction  is  going  on,  a  small  beaker,  \\  inch 
high  by  i  inch  diameter,  is  cleaned,  dried,  and  weighed.  When 
the  extraction  is  finished  the  extractor  is  removed  from  the 
condenser  and  the  cartridge  case  withdrawn.  This  is  placed 
on  a  clock  glass  in  the  steam  oven  to  dry.  The  extractor  is 
replaced  on  the  condenser,  and  the  ether  in  the  flask  allowed 
to  distil  over  until  the  large  tube  (e,  fig.  37)  is  filled  to  withii; 
half-an-inch  of  the  top  of  the  syphon  ;  it  is  then  removed  from 
the  condenser.  The  flask  is  taken  off  from  below,  and  the 
ether  poured  out  of  the  extractor  into  the  ether  bottle.  The 
whole  apparatus  is  replaced,  and  the  rest  of  the  ether  distilled 
off  from  the  flask  to  the  extractor.  The  flask  may  now  be 
finally  removed. 

A  small  quantity  of  oil  may  have  got  on  to  the  cork  of  the 
flask  by  the  too  rapid  boiling  of  the  ethereal  solution.  The 
cork  and  tip  of  the  extractor  should  be  washed  with  a  fine 
spray  of  ether,  allowing  the  washings  to  flow  into  the  flask. 

142.  The  next  operation  is  to  remove  the  oil  into  the 
weighed  beaker.  The  sides  of  the  flask  are  washed  down  with 
a  fine  spray  of  ether  delivered  from  the  jet  of  a  wash  bottle 
until  about  i  c.c.  of  liquid  has  collected  in  the  flask.  The 
liquid  is  poured  into  the  beaker.  This  operation  is  repeated 
four  or  five  times,  when  all  the  oil  will  have  been  washed  away. 
Some,  however,  will  have  crept  over  the  lip  of  the  flask,  there- 
fore the  outside  of  the  neck  should  be  sprayed,  allowing  the 
ether  to  drip  into  the  beaker. 

The  ether  is  allowed  to  evaporate  by  placing  the  beaker  on 


143]  Quantitative  Analysis  of  Oil  Cakes  97 

top  of  the  steam  oven,  overheating  being  prevented  by  placing 
two  or  three  filter  papers  between  the  beaker  and  the  metallic 
surface  of  the  oven. 

When  the  ether  has  all  gone,  the  beaker  is  heated  inside 
the  steam  oven  until  it  ceases  to  lose  weight.  The  difference 
between  this  final  weight  and  the  weight  of  the  beaker  gives 
the  weight  of  the  oil. 

143.  Estimation  of  Woody  Fibre.— The  portion  of  cake 
which  has  been  extracted  with  ether  and  dried  in  the  cartridge 
case  is  used  for  this  estimation.  It  is  transferred  to  a  i6-oz. 
beaker.  If  a  portion  adhere  to  the  filter  paper  it  may  be 
removed  by  opening  the  case  and  rubbing  the  adhering  sub- 
stance off  with  another  part  of  the  paper.  When  it  is  all  in 
the  beaker  50  c.c.  of  a  5  per  cent,  solution  of  sulphuric  acid 
are  added,  together  with  75  c.c.  of  distilled  water.  The  beaker 
is  placed  over  a  Bunsen  burner,  and  the  liquid  raised  to  a  boil. 
As  it  approaches  the  boiling-point  it  must  be  watched  care- 
fully, as  it  has  a  tendency  to  froth  up  and  boil  over.  As  soon 
as  the  frothing  starts  it  should  be  stirred  rapidly  with  a  glass 
rod,  and,  if  the  frothing  become  too  violent,  removed  for  a 
moment  from  the  burner.  When  all  frothing  has  ceased  any 
particles  of  cake  which  adhere  to  the  side  are  washed  down 
into  the  liquid  with  a  small  quantity  of  hot  water,  and  the 
solution  is  allowed  to  boil  gently  for  half-an-hour.  As  the 
liquid  becomes  more  concentrated  on  boiling,  it  is  necessary 
to  add  a  little  hot  water  from  time  to  time.  The  level  of  the 
surface  of  the  liquid  may  be  marked  by  sticking  a  piece  of 
gummed  paper  on  the  outside  of  the  beaker.  It  will  then  be 
easy  to  see  when  more  water  ought  to  be  added.  At  the  end 
of  the  half-hour  the  beaker  is  filled  up  with  cold  water  and 
allowed  to  stand  for  an  hour. 

A  clean  piece  of  linen  is  placed  over  the  top  of  a  beaker,  or, 
better,  a  strong  jam  pot  of  about  20  oz.  capacity.     The  liquid 

H 


98 


A  nalysis  of  Feeding  Materials 


[143 


in  the  beaker  is  decanted  through  this  linen.  The  solid 
matter  on  the  linen  is  washed  back  into  the  beaker  with  hot 
water.  Fifty  c.c.  of  5  per  cent.  KHO  solution  are  added,  and 
then  water  up  to  the  126-c.c.  mark.  The  beaker  is  returned 
to  the  burner  and  the  liquor  boiled  for  half-an-hour,  filled  with 
cold  water,  and  allowed  to  stand  as  before. 

The  remaining   solid   matter,  which  contains  only  woody 
fibre  and  sand,  is  filtered  off  by  means  of  the  linen  and  well 

washed  :  firstly,  three 
times  with  hot  water ; 
secondly,  once  with  di- 
lute HClj  thirdly,  three 
times  with  hot  water; 
and,  lastly,  twice  with  al- 
cohol. 

Filtration  may  be  very 
much  hastened  by  draw- 
ing the  linen  tightly  over 
the  edges  of  the  pot,  as  shown  in  fig.  39.  This  causes  a 
partial  vacuum  below,  and  the  pressure  of  the  air  above  forces 

the  liquid  through  the 
cloth. 

The  next  operation  is 
to  transfer  the  fibre  to  a 
weighed  porcelain  capsule, 
which  requires  some  little 
dexterity. 

As  much  of  the  alco- 
hol as  possible  is  squeezed 
out,    and     the    cloth    is 


Fig.  39. 


Fig.  40. 


stretched  on  a  tile,  holding  it  as  in  fig.  40.  The  fibre  is 
removed  with  the  tip  of  a  steel  spatula  and  placed  in  the 
weighed  capsule,  care  being  taken  to  scrape  all  the  substance 


144,  145]      Quantitative  Analysis  of  Oil  Cakes  99 

off  the   stretched   linen.     The  capsule  is  dried  in  the  steam 
oven  until  it  ceases  to  lose  weight. 

The  fibre  thus  estimated  will  contain  whatever  sand  there 
is  in  the  3  grams  of  cake  used.  It  is  therefore  transferred  to 
a  weighed  platinum  dish,  burned,  and  the  weight  of  the  ash 
taken.     This  is  subtracted  from  the  total  weight  of  the  fibre. 

144.  Albuminoids. — If  the  percentage  of  nitrogen  be 
multiplied  by  6*25,  the  percentage  of  albuminoid  matter  is 
obtained.  ^ 

It  is,  therefore,  only  necessary  to  estimate  the  nitrogen  in 
the  cake.  This  is  done  by  either  the  soda  lime  (paragraphs 
86-89)  or  the  sulphuric  acid  process  (paragraphs  90-95),  using 
about  I  gram  of  the  cake. 

145.  Remarks  on  Cake  Analysis.— Should  the  opera- 
tions described  in  paragraphs  137-144  be  performed  one  after 
the  other  in  the  order  given,  it  would  take  a  very  long  time  to 
complete  the  whole  analysis.  The  following  method  of  proce- 
dure will  enable  the  student  to  complete  the  analysis  in  the 
minimum  time : 

1.  Weigh  out  three  portions  of  the  ground-up  sample  as 
follows  : 

{a)  About  2  grams  in  a  porcelain  capsule. 
{b)  About  3  grams  on  a  watch  glass. 
{c)  About  I  gram  on  a  watch  glass. 

2.  Place  {a)  in  the  steam  oven. 

3.  Put  if)  in  a  flask  with  strong  sulphuric  acid  to  estimate 
the  nitrogen. 

4.  Prepare  the  Soxhlet's  apparatus,  and  start  the  oil  estima- 
tion with  ip). 

'  This  factor  6-25  is  based  on  the  fact  that  the  average  percentage  of 
nitrogen  in  the  albuminoids  of  vegetable  foods  is  16%. 

io3-m6  =  6'25. 

H2 


ICX) 


Analysis  of  Feeding  Materials         [146,  147 


The  order  in  which  the  rest  of  the  operations  should  be 
taken  depends  very  much  on  the  operator. 

146.  Method  of  Entry. — The  student  should  describe 
in  his  note  book  the  operations  performed,  and  in  entering 
data  should  use  one  page  for  weights  and  reserve  the  page 
facing  it  for  calculation  of  percentages. 

After  calculating,  the  results  of  analysis  are  entered  as 
follows : 


Moisture        .... 
Oil 

♦Albuminoid  compounds  . 

Mucilage,  starch,  &c. 

Woody  fibre.         .         . 
fAsh 

Good 

linseed 
cake 

Bad 
linseed 
cake 

Cotton 
cakeunde- 
corticated 

8-69 

5-30 

26-00 

29-50 

25-67 

4-84 

Cotton 
cake  de- 
corticated 

9-45 

13-20 

26-31 

36-02 

8-61 

6-41 

100-00 

14-05 
8 -80 
23-72 
32-87 
10-71 
9.85 

8-IO 

11-67  , 

41-94 

25-41 

4-63 

8-25 

100-00 

lOO'OO 

100-00 

♦Containing  nitrogen 
f  Containing  sand     . 

4-21 
1-40 

3-79 
5-20 

4-16 

6-71 

These  analyses  are  typical. 


Qualitative   Examination 


147.  Although  the  feeding  value  of  an  oil  cake  depends 
very  largely  on  the  percentage  of  oil  and  albuminoid  com 
pounds  which  it  contains,  still  two  cakes  which  give  identical 
analyses  may  vary  in  value  on  account  of  their  condition^ purity^ 
and  taste. 

The  condition  may  be  judged  by  breaking  up  the  cake  and 
noting  its  hardness  and  structure. 

The  purity  cannot  be  determined  without  careful  micro- 
scopic examination,  though  there  are  one  or  two  tests  by  means 


148,  U9]     Qualitative  Examinhtion  of  Oil  Cakes        loi 

of  which  injurious  substances  may  be  detected.  These  are 
given  below. 

The  taste  is  the  most  difficult  property  of  all  to  give 
an  opinion  upon,  unless  the  cake  have  a  distinctly  nasty 
taste,  in  which  case  the  analyst  should  make  some  remark 
thereon. 

148.  Testing  Linseed  Cakes.— Linseed  cake  should 
be  rich  in  mucilage  and  free  from  starch.  Both  of  these  pro- 
perties are  readily  tested.  Five  grams  of  the  ground  sample 
are  weighed  out  on  a  rough  balance  and  placed  in  an  8-oz. 
beaker.  A  hundred  c.c.  of  boiling  water  are  poured  over 
the  cake,  and  the  pasty  mass  is  stirred  for  a  few  moments, 
then  allowed  to  stand  for  about  ten  minutes.  A  rich  linseed 
cake  will,  when  treated  in  this  manner,  settle  down  into  a 
jelly-like  mass,  whilst  a  poor  cake  will  settle  down  in  a 
more  granular  state.  By  experimenting  with  a  few  samples 
the  student  will  readily  see  the  value  of  this  test  in  judging  the 
mucilaginous  properties  of  the  cake.  To  test  for  starch,  a 
little  of  the  hot  liquor  with  the  cake  in  suspension  is  poured 
into  a  test  tube  and  boiled  smartly  for  a  few  moments.  It  is 
then  cooled  down,  and  when  quite  cold  a  few  drops  of  a  solu- 
tion of  iodine  in  alcohol  are  added.  The  emulsion  should 
only  become  slightly  blue.  If  it  become  dark  blue  some 
starchy  material  is  present. 

149-  Microscopic  Examination. —The  student  should 
prepare  and  mount  for  himself  specimens  of  the  husks  of  the 
various  seeds  occurring  in  feeding  materials,  and  make  him- 
self familiar  with  the  appearance  of  each.  The  following 
method  will  be  found  useful  in  preparing  the  husk  of  the  seed 
for  examination  : 

Digest  a  portion  (about  5  grams)  of  the  material  with  dilute 
sulphuric  acid  (2  per  cent.)  on  the  water  bath  for  half-an-hour. 
Remove  the  acid  liquid  by  decantation,  and  wash  several  times 


I02  Analysis  of  Feeding  Materials  [150-153 

in  the  same  manner.  Next  digest  with  equally  dilute  caustic 
alkali,  and  repeat  the  washing.  This  renders  the  texture  of  all 
those  seeds  commonly  met  with  in  cattle  foods,  and  the  impu- 
rities occurring  with  them,  sufficiently  transparent  to  be  readily 
recognised  under  the  microscope.  After  washing  the  alkaline 
liquid  away,  it  is  sometimes  an  advantage  to  wash  the  material 
with  dilute  hydrochloric  acid,  which  reduces  the  strong  colour 
produced  by  the  alkali. 

Another  method  which  produces  the  same  effect  is  to  place 
the  substance  on  a  slip  of  glass,  add  a  drop  of  glycerin,  and 
heat  until  the  glycerin  begins  to  boil.  The  glycerin  is  with- 
drawn by  means  of  filter  paper,  and  the  operation  repeated 
until  sufficient  transparency  is  attained. 

ANALYSIS   OF   FEEDING   MEALS 

150.  Feeding  meals  are  usually  analysed  in  exactly  the 
same  way  as  oil  cakes,  excepting  that  the  carbohydrates,  and 
in  the  case  of  flour  the  gluten,  are  occasionally  estimated. 

151.  Starch. — This  may  be  estimated  roughly  by  knead- 
ing 5  grams  of  the  meal  with  a  little  water  on  a  piece  of  linen, 
such  as  is  used  in  the  estimation  of  woody  fibre,  and  washing 
thoroughly  with  water.  The  starch  will  pass  through  the  cloth 
with  the  filtrate.  This  must  be  allowed  to  settle,  then  the 
starch  filtered  off  on  a  weighed  filter,  washed,  dried  at  a  low 
temperature,  and  weighed. 

152.  A  more  scientific  method  of  procedure  is  to  convert 
the  starch,  inuline,  and  dextrin  into  sugar,  and  estimate  that  as 
described  in  paragraphs  82-84.  The  starch  is  converted  into 
sugar  by  means  of  diastase. 

153.  Preparation  of  Diastase. — Place  about  5  lbs.  of 
malt,  finely  ground,  in  a  large  beaker,  and  just  cover  it  with 


154-156]  Analysis  of  Feeding  Meals  103 

water.  Allow  to  stand  four  hours.  Squeeze  the  liquid  from 
this  pulp  through  a  bag  of  fine  linen.  (The  press  shown  in 
fig.  43  would  be  admirable  for  this  purpose.)  Filter  if  neces- 
sary. Add  strong  alcohol  until  a  white  precipitate  (diastase) 
forms.  Filter,  wash  with  alcohol.  Press  the  precipitate  be- 
tween folds  of  cloth  until  as  dry  as  possible,  transfer  to  a  dish, 
and  place  in  an  exhausted  receiver  until  quite  dry.  Bottle  the 
powder,  and  keep  in  a  cool  dry  place. 

154.  The  Analysis. — Weigh  out  1-5  gram  of  the  meal. 
Mix  with  a  little  water  in  a  6-oz.  beaker,  add  50  c.c.  of  boiling 
water,  stirring  well  meanwhile.  Place  the  beaker  on  the  water 
bath  until  all  clots  have  been  thoroughly  broken  down,  then 
cool  down  to  62°  C.  and  add  about  30  milligrams  of  diastase 
powder  dissolved  in  a  few  c.c.  of  water.  Keep  at  62°  to  65°  C. 
for  about  an  hour  by  standing  on  the  water  oven.  This  will 
convert  the  whole  of  the  starch  into  dextrin  and  maltose. 
Filter  off  the  liquid,  and  dilute  to  250  c.c.  Measure  off  50  c.c.  of 
this  solution  into  a  beaker,  add  2  c.c.  of  sulphuric  acid  (i  to  8), 
and  heat  in  the  water  bath  for  four  hours,  adding  water  from 
time  to  time  as  the  liquid  evaporates.  Then  neutralise  with 
KHO,  make  up  to  100  c.c,  and  estimate  the  glucose  as  de- 
scribed in  paragraphs  82-84. 

155.  Gluten  in  Flour. — Weigh  out  about  30  grams  of 
flour,  knead  to  a  paste  with  water,  and  transfer  to  a  linen  fibre 
cloth — or,  better,  fine  silk.  Tie  it  up  like  a  pudding,  and  knead 
with  the  fingers  under  clear  water  until  no  further  starch  comes 
out.  This  may  be  recognised  by  its  no  longer  turning  the 
water  milky.  Remove  gluten  as  described  in  the  case  of  woody 
fibre  (fig.  40),  keeping  the  spatula  wet  all  the  time.  Roll  the 
gluten  into  a  ball  with  wet  fingers,  wash  thoroughly  in  water, 
wipe  off  any  moisture,  and  weigh. 

156.  A  few  typical  analyses  oi  feeding  meals  are  appended. 


104 


Analysis  of  Feeding  Materials  [157,  15  8 


Rice 
meal 

Malt 
dust 

Barley 
meal 

Palm  nut 
meal 

Maize 
meal 

Wheat 
sharps 

11-68 

4-73 

15-50 

59-88 

4-47 

3-74 

Moisture 

Oil         .         .         . 
♦Albuminoid  com- ' 
pounds 

Carbohydrates,  kc. . 

Woody  fibre  . 
fAsh 

10-30 

9-31 

13-06 

53-97 
6-12 
7-24 

9-30 
1-40 

22-88 

47-54 
11-83 
7-05 

loo-co 

io-8i 
2-90 

12-76 

63-59 
6-30 

3-64 

9-24 
8-27 

15-75 
47-76 
14-13 

4-85 

12-93 
4-30 
9-94 

68-73 
2 -60 
1-50 

100-00 

100-00 

100-00 

100-00 

100 -oo 

*Containing  nitrogen 
f  Containing  sand 

2-09 

3-66 
2-35 

2-04       2-52 

1-59 

2-48 
•78 

ANALYSIS   OF   GRASS    AND   HAY 

157.  These  substances  are  not  often  analysed  for  com- 
mercial purposes,  but  it  is  sometimes  necessary  for  experimental 
work  to  find  the  relative  values  of  different  samples  of  grass 
and  hay.  A  certain  amount  of  information  may  be  gained  by 
treating  the  samples  as  though  they  were  oil  cakes.  It  must 
be  remembered,  however,  that  in  the  case  of  substances  con- 
taining green  colouring  matter  this  will  be  to  a  great  extent 
extracted  by  ether  along  with  the  fat. 

The  method  of  analysis  about  to  be  described  gives  all  the 
information  concerning  a  sample  which  is  likely  to  be  required. 

If  the  student  reads  through  this  description,  and  the 
following  one — analysis  of  roots — he  will  see  that  both  of  them 
are  very  long  and  very  tedious.  He  is  therefore  advised  to 
miss  these  two  analyses  for  the  present  and  return  to  them  after 
he  has  completed  the  section  on  manures. 

When  performing  the  analyses  many  long  intervals  will 
occur  during  which  the  operator  has  to  wait.  There  is  no 
need  to  be  idle,  as  soil  analysis  may  be  started  during  these 
waits. 

158.  Moisture. — It  is  of  great  importance  that  the  water 


158] 


Analysis  of  Grass  and  Hay 


los 


in  grass  be  estimated  as  soon  as  possible  after  the  sample  has 
been  taken,  otherwise  much  will  be  lost  by  evaporation.  It  is 
best  to  weigh  out  all  the  portions  required  for  different  parts 
of  the  analysis  immediately  after  the  grass  or  hay  has  been 
cut  up.     The  following  portions  should  be  weighed  out : 

20  grams  of  hay,  or 
50  „         grass 

S  grams  of  hay,  or  .^^^j^^ 

10  „        grass    J 

10  grams  of  hay,  or 
40  „         grass 


\  for  moisture ; 


for  crude  fibre. 


These  substances  are  somewhat  too  bulky  to  weigh  out  on 
a  delicate  balance  ;  therefore  a  large  balance,  such  as  is  repre- 


sented in  fig.  41,  is  used.     It  must  be  capable  of  discerning 
•005  gram. 

The  moisture  portion  is  weighed  out  in  a  sheet  of  filter 
paper  which  has  been  folded  to  form  a  sort  of  bag  for  holding 
the  grass.  Instead  of  weighing  the  filter  paper  to  begin  with, 
it  should  be  counterpoised  by  placing  a  similar  piece  in  the 
other  scale  pan,  and  cutting  off  bits  of  the  heavier  one  until 
both  pieces  are  of  the  same  weight.     Both  pieces  of  paper 


io6  Analysis  of  Feeding  Materials         [159,  160 

are  dried  in  exactly  the  same  way.     They  are  heated  together 
in  the  steam  oven  until  the  hay  ceases  to  lose  weight. 

When  the  moisture  has  been  determined,  the  dry  matter 
left  in  the  filter  paper  is  ground  up  finely  in  a  laboratory  mill, 
bottled,  and  labelled  '  Dry  matter.'  This  operation  is  greatly 
facilitated  by  placing  the  hay  in  the  water  bath  for  a  few 
minutes  after  it  has  been  finally  weighed,  and  then  grinding 
whilst  hot,  as  it  is  then  much  more  brittle  than  when  cold. 

159.  Woody  Fibre. — The  portion  which  has  been 
weighed  out  for  this  estimation  is  placed  in  a  20-oz,  beaker 
and  treated  exactly  as  described  in  the  case  of  oil  cakes,  para- 
graph 143,  except  that  in  each  digestion  double  the  quantity 
of  liquid  is  used.  After  the  fibre  has  been  transferred  to  the 
cloth  it  will  often  contain  green  colouring  matter.  This  should 
be  removed  by  soaking  for  an  hour  in  alcohol,  then  for  another 
hour  in  ether.  It  is  then  transferred  to  a  small  weighed  beaker, 
dried,  and  weighed.  The  ash  in  the  fibre  should  be  deter- 
mined and  subtracted  from  the  total  weight. 

160.  Crude  Fibre. — The  portion  weighed  out  is  placed 
in  a  20-oz.  beaker.  The  beaker  is  filled  up  with  water  and 
allowed  to  stand  twenty-four  hours.  The  liquid  is  decanted 
off  and  rejected.  The  beaker  is  filled  up  again,  allowed  to 
stand  three  hours,  and  decanted.  A  third  soaking  is  made  for 
one  hour.  It  next  has  to  be  treated  with  hot  water.  The  total 
washing  is  as  follows  : 

24  hours  in  cold  water ; 

3  J>  >J  »  5J 

I     >>       »       >j       »j 

\    „      „     hot     „     (four  times) 

After  these  soakings  have  been  performed,  boil  for  a  minute 
with  water  twice.  When  decanting  it  is  difficult  to  remove 
most  of  the  water.     This,  however,  may  be  accomplished  by 


161,  162]  Analysis  of  Grass  and  Hay  107 

placing  a  disc  of  glass  just  inside  the  beaker,  and  squeezing  as 
shown  in  fig.  42. 

After  this  treatment  all  matter  which  is  soluble  in  water 
will  have  been  removed.  It  remains  now  to  extract  the 
colouring  matter.  This  often  takes 
some  time.  It  is  done  by  soaking  in 
alcohol  for  an  hour  at  a  time,  straining 
off  the  spirit  after  each  soaking  until 
it  runs  off  colourless.  Ether  is  then 
used  until  the  fibre  is  quite  white.  It 
is  then  dried  and  weighed  in  the  same 
manner  as  the  woody  fibre.  '  ''^' 

Considerable  annoyance  is  frequently  caused  in  this  opera- 
tion by  the  evaporation  of  the  ether,  especially  when  the  fibre 
is  allowed  to  soak  over  night.  This  may,  to  a  very  great 
extent,  be  prevented  by  placing  over  the  mouth  of  the  beaker 
half-a-dozen  thicknesses  of  filter  paper,  covering  these  with 
a  glass  disc,  and  placing  a  small  weight  on  the  top  of  the  disc. 
In  this  way  the  beaker  is  made  fairly  air-tight,  and  much  less 
loss  occurs  than  when  the  beaker  is  merely  covered  with  a 
clock  glass. 

The  crude  fibre  must  be  ground  up,  bottled,  and  labelled. 

So  far  the  only  constituents  which  have  been  estimated  are 
moisture,  woody  fibre,  and  crude  fibre.  The  two  bottled  por- 
tions may  now  be  proceeded  with. 

Analysis  of  the  *  Dry  Matter  ' 

161.  Before  any  portion  is  weighed  out,  the  'dry  matter' 
must  be  heated  in  the  steam  oven  for  an  hour  and  cooled  in 
the  desiccator.  This  is  necessary,  as  the  powdered  substance 
is  very  hygroscopic. 

162.  Total  Nitrogen. — Weigh  out  about  2  grams  of  the 


io8  Analysis  of  Feeding  Materials  [163-165 

freshly  dried  substance,  and  estimate  the  nitrogen  by  the  acid 
process  (paragraphs  90-95).  The  flask  must  be  carefully 
watched  whilst  heating,  as  the  acid  is  apt  to  froth.  Should 
the  solution  take  a  long  time  to  clear,  it  may  be  hastened 
by  adding  a  drop  of  mercury.  If  this  be  done,  the  mercury 
must  be  precipitated  by  adding  sufficient  potassium  sulphide 
along  with  the  caustic  soda  before  distilling  off  the  ammonia. 
Otherwise  mercury  ammonium  compounds  are  often  formed 
which  are  not  completely  decomposed  by  NaHO  (see  para- 
graph 93). 

163.  Total  Albuminoids. — Weigh  out  2  grams  of  freshly 
dried  '  dry  matter,'  place  it  in  a  4-oz.  beaker,  and  fill  the  beaker 
with  4  per  cent,  carbolic  acid  solution  in  water.  Add  a  drop  of 
meta-phosphoric  acid  and  allow  to  soak  for  twenty-four  hours. 
Decant  the  liquid  through  a  filter  paper,  and  boil  up  the  residue 
with  a  fresh  portion  of  the  carbolic  acid  solution.  Filter,  wash 
three  or  four  times  with  carbolic  acid,  and  dry.  This  treatment, 
whilst  coagulating  all  the  albuminoids  and  rendering  them 
insoluble,  dissolves  all  the  amides. 

When  the  substance  is  dry  introduce  it,  together  with  the 
filter  paper,  into  an  8-oz.  flask,  and  estimate  the  nitrogen  by  the 
acid  process  (paragraphs  90-95). 

164.  Total  Ash. — Weigh  out  2  grams  of  freshly  dried 
substance  into  a  platinum  dish,  and  determine  the  ash  as  in  a 
sample  of  oil  cake. 

Analysis  of  the  Crude  Fibre 

165.  Insoluble  Albuminoids.— All  the  amides  being 
soluble  in  water,  the  insoluble  albuminoids  may  be  calculated 
from  the  nitrogen  in  the  crude  fibre.  Weigh  out  2  grams  of 
freshly  dried  crude  fibre,  and  determine  the  nitrogen  in  the 
same  way  as  has  been  done  in  the  dry  matter. 


166-168]  Analysis  of  the  Crude  Fibre  109 

166.  Insoluble  Ash. — Weigh  out  2  grams  of  dry  crude 
fibre  in  a  platinum  dish,  and  determine  the  ash  as  before. 

167.  Calculation. — First   calculate   from   the  weights  of 
different  substances  the  following  percentages  : 

Percentage  of  moisture  \ 

„  woody  fibre  \  in  the  sample ; 

crude  fibre  ) 

total  nitrogen  \ 

albuminoid  nitrogen  \  in  the  dry  matter ; 
ash  J 


»  °  I    in  the  crude  fibre, 

ash  ] 


Work  out  the  percentages  of  albuminoids  contained  in  the 
dry  matter  and  crude  fibre  respectively  by  multiplying  the  per- 
centages of  albuminoid  nitrogen  by  6*25. 

Reduce  all  the  percentages  to  parts  per  hundred  of  the 
total  sample,  thus : 

percentage  of  ash  in  dry  matter  x  percentage  of  dry  matter 

100 

=  percentage  of  ash  in  sample. 

Likewise 

percentage  of  ash  in  crude  fibre  x  percentage  of  crude  fibre 

100 

=  percentage  of  insoUible  ash  in  sample. 

Make  the  following  additions  and  subtractions  : 

Total  nitrogen  —  albuminoid  nitrogen  =  amide  N  ; 
Total  albuminoids  —  insoluble  albuminoids  =  soluble  albuminoids  ; 
Total  ash  —  insoluble  ash  =  soluble  ash ; 

Crude  fibre  —  (insoluble  albuminoids  +  woody  fibre  +  insoluble  ash) 
=  digestible  fibre. 

168.  The  following  figures,  taken  from  actual  analyses  of 
grass  and  hay,  show  the  method  of  entering  results. 


no 


Analysis  of  Feeding  Materials         [169,  170 


Moisture     ...... 

Soluble  albuminoids    .... 

Insoluble  albuminoids .... 

Digestible  fibre   ..... 

Woody  fibre         ..... 

Soluble  ash  ..... 

Insoluble  ash       ..... 

♦Chlorophyll  amides,  &c.  (by  difference) 

♦Containing  nitrogen     .... 
Total  nitrogen     ..... 


Grass 

Hay 

69-34 

14-00 

o-ii 

•98 

2-30 

7*89 

IO-39 

28-68 

8-53 

22-92 

1-34 

2-20 

•87 

4-66 

7-12 

18-67 

IQO'QO 

lOO-OO 

•12 

•12 

•50 

1-54 

SILAGE 

169.  The  analysis  of  this  substance  is  conducted  in  much  the 
same  way  as  that  of  hay  and  grass,  using  the  same  quantities  of 
substance  as  for  grass.  The  only  difference  is  that  the  acidity 
is  estimated  in  addition  to  the  constituents  given  above. 

This  is  done  in  the  40  grams  weighed  out  for  the  estimation 
of  crude  fibre. 

170.  Acidity. — The  liquids  from  the  first  three  soakings  (see 

paragraph  t6o)  are  collected  and  made  up  to  a  litre  with  distilled 

water.     Five  hundred  c.c.  are  taken,  and  the  total  acidity  deter- 

N 
mined  with       KHO.     It  is  a  matter  of  some  difficulty  to  de- 
10 

tect  the  exact  point  of  neutrality  owing  to  the  greenish  colour  of 
the  solution.  A  dozen  drops  of  phenol-phthalein  are  placed  with 
a  stirring  rod  on  different  parts  of  a  glass  plate.  The  alkali  is 
run  into  the  liquid,  a  few  drops  at  a  time.  After  each  addition 
it  is  stirred  vigorously,  and  tested  by  touching  one  of  the  drops 
on  the  plate  with  a  drop  of  the  liquid  on  the  end  of  the  rod. 
When  the  indicator  gives  a  faint  pink  reaction  the  quantity  of 
potash  added  must  be  read  off. 

The  remaining  500  c.c.  are  boiled  down  in  a  beaker  over  a 


171-173] 


Silage 


III 


Bunsen  until  only  50  c.c.  are  left ;  this  volatilises  all  the  acetic 
acid.  About  200  c.c.  of  water  are  added,  and  the  liquid 
titrated  as  before. 

171.  Calculation. — The  number  of  c.c.  used  in  the  second 
titration  are  subtracted  from  the  number  used  in  the  first.  The 
difference  gives  the  potash  required  to  neutralise  the  volatile 
acids.  These  are  calculated  by  taking  the  amount  of  acetic 
acid,  CH3CO2H,  equivalent  to  the  potash. 

From  the  second  equation  the  non-volatile  acids  are  calcu- 
lated as  lactic  acid,  C2H4(OH)C02H. 

172.  The  following  are  typical  analyses  of  silage  : 


Sour 


Sweet 


Water 
Acetic  acid 
Lactic  acid 
Soluble  ash 
Insoluble  ash 
Soluble  albuminoids    . 
Insoluble  albuminoids 
Digestible  fibre   . 
Woody  fibre 
♦Chlorophyll,  &c. 

*Containing  nitrogen 
Total  nitrogen 


64-31 
•49 
•96 

1-51 

1-37 

•96 

1-86 

777 
11-46 

9-31 


67-33 

•07 

•60 

I -02 

1-35 
•60 
1-88 
8-66 
8-91 
9-58 


100 -oo 


•23 
•67 


ROOTS,   SWEDES,   MANGELS,   TURNIPS,   &c. 

173.  This  analysis  is  conducted  in  a  somewhat  peculiar 
manner,  and  requires  a  slight  preliminary  explanation. 

The  constituent  parts  of  roots  may  be  divided  into  the  in- 
soluble and  the  soluble  portions  ;  but  seeing  that  the  water  in 
these  plants  amounts  to  between  80  and  90  per  cent.,  it  is  to 
be  expected  that  the  whole  of  the  soluble  matter  will  be  in 
solution.     The  analysis,  therefore,  divides  itself  into  two  parts — 


112  Analysis  of  Feeding  Materials         [174,  175 

namely,  the  analysis  of  the^  juice  or  soluble  portion,  and  the 
analysis  of  the  crude  fibre  or  insoluble  portion. 

From  the  sample  it  is  therefore  necessary  to  procure  two 
sub-samples,  one  of  the  juice  and  one  of  the  insoluble  matter. 
These  two  must  be  analysed  separately,  in  the  same  way  as  the 
different  parts  of  hay  or  grass  are  worked  upon.  And  just  as 
happens  in  the  case  of  hay,  &c.,  the  first  thing  to  be  estimated 
in  roots  is  the  moisture,  which  leads  to  the  following 

Preliminary   Treatment 

174.  Take  three  or  four  average-sized  roots,  and  split  each 
with  a  clean  knife  into  eight  pieces.  Take  one  of  these  piece's 
from  each  root.  Cut  the  portions  into  thin  shoes,  and  weigh 
out  about  100  grams  of  the  slices  in  the  rough  balance  as 
described  in  paragraph  158.  When  weighed  spread  the  slices 
out  on  the  filter  paper,  and  dry  them  in  the  air  oven  at  60°  C. 
until  they  become  shrivelled  up.  The  slices  will  now  be  hard 
and  fairly  brittle.  Break  them  up  as  finely  as  can  conve- 
niently be  done  by  hand,  and  then  dry  in  the  steam  oven  until 
no  further  loss  in  weight  takes  place. 

This  operation  takes  up  three  or  four  days.  It  will  take 
considerably  longer  if  the  oven  be  allowed  to  cool  during 
the  night,  as  the  partially  dried  material  is  very  hygroscopic, 
and  absorbs  a  considerable  amount  of  water  whilst  the  oven  is 
cold.  In  laboratories  where  the  ovens  do  not  keep  hot  day 
and  night  matters  may  be  considerably  hastened  by  removing 
the  substance  from  the  oven  to  a  desiccator  every  evening,  and 
returning  to  the  oven  as  soon  as  it  is  warm  in  the  morning. 

175.  The  moisture,  however,  is  not  the  only  constituent 
which  must  be  estimated  in  the  fresh  root.  The  two  principal 
portions,  as  mentioned  above,  are  the  crude  fibre  and  the 
juice.     If  one  of  these  be  estimated,  the  other  may  be  calcu- 


176,  177]        Preliminary   Treatment  of  Roots 


113 


lated  by  difiference.     Therefore  we    estimate  the   crude  fibre 
directly  and  the  juice  by  difference,  analysing  samples  of  both. 

176.  Estimation  of  Crude  Fibre.— When  the  roots 
are  split  up  into  eighths,  a  section  of  each  is  taken  for  this 
estimation.  The  portions,  however,  are  not  weighed,  but  are 
rubbed  down  on  a  bread-grater  as  rapidly  as  possible,  so  as  to 
obtain  a  pulp  before  any  evaporation  has  taken  place.  When 
a  sufficient  amount  has  been  pulped, 
about  1,000  grams  are  weighed  out 
on  a  large  clock  glass,  transferred 
to  a  linen  bag,  and  placed  in  a 
press.  The  object  of  this  press  is 
to  get  a  fair  sample  of  the  juice. 
It  has  been  found  by  experiment 
that  the  first  portions  of  the  juice 
to  be  squeezed  out  are  very  slightly 
different  from  the  last ;  hence  al- 
though for  very  accurate  analyses 
it  is  necessary  to  squeeze  out  most 
of  the  juice,  still,  should  a  powerful 
press  be  unobtainable,  a  very  good 
result  may  be  got  by  pressing  out 
a  small  amount  of  the  liquid. 

177.  An  ordinary  cheese  press 
may  be  utilised  for  separating  the 
juice,  if  a  little  extra  apparatus  be 
added  to  it.  Fig.  43  shows  a  press,  on  the  table  of  which  is 
placed  a  cylinder,  a,  to  hold  the  pulp.  Into  this  is  fitted  a 
plunger,  b.  Around  the  bottom  part  of  the  cylinder  holes  are 
drilled  to  allow  the  juice  to  escape. 

The  linen  bag  containing  the  weighed  quantity  of  pulp  is 
squeezed  in  the  press  until  as  much  juice  as  possible  has  been 
obtained.     The  juice  is  collected  in  wide-mouthed  bottles,  and 


Fig.  43. 


114  Analysis  of  Feeding  Materials         [i 78-180 

corked  up  for  analysis.  Not  that  this  analysis  may  be  deferred 
for  any  length  of  time ;  in  fact,  the  portions  of  juice  for  different 
operations  must  be  measured  out  as  soon  as  the  quantities  for 
crude  and  woody  fibre  have  been  weighed  from  the  pulp. 

178.  When  no  further  juice  can  be  pressed  out,  loosen  the 
press,  remove  the  bag,  place  it  on  a  counterpoise  clock  glass, 
and  weigh  on  the  '  rough  '  balance.  The  next  three  weighings 
must  be  performed  as  rapidly  as  possible,  to  prevent  loss  by 
evaporation.     They  are  as  follows  : 

Weigh  out  50  grams  of  the  pressed  pulp  for  crude  fibre. 

Weigh  out  10  grams  of  the  pressed  pulp  for  woody  fibre. 

Remove  the  rest  of  the  pulp  completely  from  the  linen  bag, 
and  weigh  the  bag  whilst  still  moist. 

All  these  weighings  may  be  performed  on  the  rough 
balance. 

Treat  the  two  portions  of  pulp  thus  weighed  out  for  crude 
and  woody  fibre  exactly  as  though  they  were  samples  of  hay, 
except  that  the  washings  with  ether  and  alcohol  are  un- 
necessary, as  the  pulp  contains  little  or  no  colouring  matter. 
When  these  have  been  started,  proceed  at  once  to  the  analysis 
of  the  juice. 

Analysis   of   the   Juice 

179.  The  substances  to  be  estimated  in  the  juice  are  total 
solids  in  the  juice,  soluble  albuminoids^  glucose^  cane  sugar,  and 
soluble  ash. 

To  save  the  trouble  of  weighing  out  separate  portions,  it  is 
usual  to  take  the  specific  gravity  of  the  juice  and  measure  out 
the  amounts  required,  calculating  the  weights  afterwards. 

180.  Since  the  juice  is  apt  to  change  in  composition  if  kept 
for  any  length  of  time,  the  immediate  treatment  of  each  portion 
is  first  described,  and  the  determination  entered  into  more  fully 


181,  182]  Analysis  of  the  Juice  I15 

afterwards.  First  get  together  the  apparatus  and  solutions 
required,  so  that  no  time  may  be  lost  after  the  work  has  once 
begun. 

Apparatus,     A  50-c.c.  pipette  ; 
A  20-c.c.  pipette ; 
A  lo-c.c.  pipette  ; 
Two  measuring  flasks,  100  c.c. ; 
A  shallow  evaporating  basin  (weighed) ; 
A  4-0Z.  beaker ; 
A  thermometer ; 
A  sp.  gr.  bottle. 

Solutions.     Saturated  solution  of  lead  acetate  ; 
Strong  lactic  acid. 

181.  Immediate  Treatment.— Note  the  temperature. 
Glucose.     Measure  out  10  c.c.  and  run  it  into  one  of  the 

loo-c.c.  flasks.  Add  about  5  c.c.  of  distilled  water,  then  10  c.c. 
of  the  lead  acetate  solution.  Make  up  to  100  c.c.  with  water, 
shake  well,  and  allow  to  settle. 

Total  Sugar.  Measure  out  20  c.c.  of  the  juice  into  the 
other  loo-c.c.  flask,  and  treat  in  exactly  the  same  way. 

Total  Solids  and  Ash.  Measure  out  50  c.c.  of  the  juice, 
and  run  into  the  evaporating  dish.  Place  this  on  the  water 
bath  to  evaporate. 

Soluble  Albuminoids.  Measure  out  50  c.c.  of  the  juice  into  a 
4-0Z.  beaker  ;  add  six  drops  of  strong  lactic  acid  ;  stir  well,  cover 
with  a  clock  glass,  and  allow  to  stand  for  twenty-four  hours. 

Take  the  temperature  of  the  juice  again. 

182.  If  these  operations  have  been  performed  with  a  fair 
amount  of  rapidity,  the  temperature  of  the  juice  will  not  have 
appreciably  changed.  This  is  of  importance,  as  any  heating 
or  cooling  of  the  juice  will  alter  its  specific  gravity,  and  the 
results  obtained  will  not  be  strictly  comparable. 

I  2 


Ii6  Analysis  of  Feeding  Materials         [183-185 

Should  the  temperature  have  altered,  the  specific  gravity  is 
taken  at  the  mean  temperature  between  the  two  readings. 

The  specific  gravity  is  determined  by  means  of  a  hydro- 
meter or  a  specific  gravity  bottle. 


Details  of  Juice  Analysis 

183.  Glucose. — The  lead  acetate  which  has  been  added 
to  the  diluted  juice  will  form  a  heavy  precipitate  with  the  sub- 
stances which  caused  turbidity,  so  that  in  the  course  of  a  few 
hours  a  perfectly  clear  solution  will  be  obtained,  all  the  precipi- 
tate having  settled  at  the  bottom  of  the  flask. 

In  a  normal  swede  this  clear  solution  will  be  of  just  aboiit 
the  correct  strength  for  treatment  with  Fehling's  solution. 
Remove  50  c.c.  from  the  flask  with  a  pipette,  taking  care  not 
to  disturb  the  precipitate,  and  transfer  to  a  clean,  dry  burette. 
Determine  the  glucose  with  Fehling's  solution  exactly  as  de- 
scribed in  paragraphs  82-84. 

184.  This  method  gives  results  sufficiently  accurate  for 
most  purposes.  If,  however,  results  are  required  of  the  highest 
possible  accuracy,  the  excess  of  lead  should  be  removed  from 
the  solution  before  titration.  In  this  case  the  sugar  solution 
should  not  be  made  up  to  100  c.c.  immediately  after  adding 
the  lead  acetate  solution,  but  should  be  allowed  to  stand  for 
two  hours  to  settle.  At  the  end  of  that  time  20  c.c.  of  a 
saturated  solution  of  alum  should  be  added.  This  will  pre- 
cipitate the  excess  of  lead.  The  solution  should  then  be  made 
up  to  100  c.c,  shaken  up,  and  allowed  to  settle.  When  quite 
clear  it  must  be  treated  as  described  in  the  last  paragraph. 

185.  Total  Sugar. — Measure  out  50  c.c.  of  the  solution, 
clarified  for  this  determination,  into  a  4-oz.  beaker,  taking  care 
as  before  not  to  remove  any  of  the  sediment.  Add  10  c.c.  of 
dilute  sulphuric  acid  (i  to  4),  and  digest  on  the  water  bath  for 


186-188]  Details  of  Juice  Analysis  117 

twenty  minutes.  Filter  into  a  loo-c.c.  flask,  and  wash  the 
precipitate  well  with  successive  small  quantities  of  hot  water 
until  the  filtrate  measures  rather  less  than  loo  c.c.  ;  neutralise 
with  KHO.  Cool  the  flask,  and  make  up  to  100  c.c.  Trans- 
fer to  a  burette,  and  determine  the  glucose  with  Fehling's 
solution  (paragraphs  82-84). 

186.  Total  Solids. — Evaporate  the  50  c.c.  measured  into 
the  dish  until  a  scum  forms  on  the  surface.  Weigh  a  piece  of 
platinum  wire  about  4  inches  long ;  bend  one  end  into  a  hook 
and  place  in  the  dish  so  that  the  hooked  end  remains  out  of 
the  liquid,  and  by  hanging  on  to  the  edge  of  the  basin  prevents 
the  wire  from  slipping  in  altogether.  This  platinum  wire  is 
used  from  time  to  time  to  break  up  the  scum  and  thus  assist 
evaporation.  When  the  whole  of  the  juice  is  reduced  to  a 
stiff  paste,  place  the  dish  in  the  steam  oven  until  it  ceases  to 
lose  weight.  This  will  occupy  two  or  three  days,  and  the  dish 
should  be  removed  to  a  desiccator  at  night  time,  or  whenever 
the  oven  is  allowed  to  cool. 

187.  Soluble  Ash.— When  the  solids  in  the  juice  no 
longer  lose  weight,  the  dish  is  heated  very  cautiously  on  an 
Argand  burner,  and  the  ash  determined  as  in  a  sample  of  oil 
cake.  Special  care  must  be  taken  to  prevent  the  charred  mass 
from  fusing. 

188.  Soluble  Albuminoids. — The  lactic  acid  which  has 
been  added  to  the  portion  measured  off  for  this  estimation  will 
precipitate  all  the  albuminoids  in  a  coagulated  state.  After 
the  liquid  has  stood  twenty-four  hours  or  more,  decant  off  the 
liquor  through  a  filter  paper,  arranged  with  a  filter  pump  as 
shown  in  fig.  15.  Remove  the  solid  matter  with  hot  water  to 
the  paper,  and  wash  well.  Dry  the  precipitate  in  the  steam 
oven.  Place  the  filter  paper  with  its  contents  in  an  8-oz.  flask, 
and  determine  the  nitrogen  by  the  acid  process. 


ii8 


Analysis  of  Feeding  Materials         [i89-i9i 


Analysis  of  the   Crude   Fibre 

189.  The  crude  fibre  is  treated  in  exactly  the  same  manner 
as  the  crude  fibre  of  hay,  estimations  being  made  of  nitrogen 
and  ash. 


Analysis   of   the   Dry   Matter 

190.  Estimate  the  ash  and  nitrogen  exactly  as  in  a  sample 
of  hay. 

191.  Calculation. — This  is  much  the  same  as  the  calcu- 
lation of  grass  analysis,  only  more  complicated.  First  calcu- 
late from  the  weight  of  different  substances  the  following 
percentages : 


Percentage  of  moisture . 
„  pressed  pulp 


„  crude  fibre 

„  woody  fibre 

„  nitrogen . 

„  ash 

„  nitrogen . 

„  ash 

„  albuminoid  nitrogen 

„  ash 

„  glucose   . 

,,  cane  sugar 

Multiply  the  percentages  of  nitrogen  in  crude  fibre  and 
juice  by  6*25  to  obtain  insoluble  and  soluble  albuminoids. 

Reduce  the  percentages  of  crude  and  woody  fibre  to  parts 
per  hundred  of  the  original  sample,  thus  : 

Percentage  of  crude  fibre  x  percentage  of  pulp 

100 

=  percentage  of  crude  fibre  in  the  sample. 


in  the  sample ; 
in  the  pressed  pulp ; 
in  the  dry  matter  ; 
in  the  crude  fibre  ; 

•in  the  juice. 


192] 


Analysis  of  Roots 


119 


Similarly  for  the  woody  fibre. 

Having  obtained  the  percentage  of  crude  fibre,  or  insoluble 
matter,  we  have  only  to  subtract  that  number  from  100  to 
obtain  the  percentage  of  juice,  which  contains  all  the  water 
and  soluble  matter. 

Next  reduce  all  the  numbers  calculated  as  percentages  of 
the  juice,  crude  fibre,  and  dry  matter  to  percentages  of  the 
root,  exactly  as  in  the  case  of  grass  (paragraph  167). 

Make  the  following  additions  and  subtractions  : 

Crude  fibre  —  (woody  fibre  +  insoluble  ash  +  insoluble  albuminoids) 
=  digestible  fibre. 


192.  The  following  analysis  of  a 

swede  sample  shows  the 

method  of  entering  results  : 

Juice,  97-466  per  cent. 
Water            | 
Amides,  &c.  \      •         '         '         ' 

.    90-020 

♦Soluble  albuminoids     . 

.       .        -167 

•    Cane  sugar 

Glucose       .         •         .         .         . 
Soluble  ash           .         .         .         . 

.        .         -817 

6-030 

•432 

P'ibre,  2-534. 

Insoluble  ash        .         .         .         . 

-205 

flnsoluble  albuminoids  . 
Digestible  fibre 
Woody  fibre      J           '         *         * 

-216 

.       2-113 

loo-ooo 

♦Containing  nitrogen 

.     -0268 

T        >'              j»            .        .        . 
Non-albuminoid  nitrogen 
Total  nitrogen      .         .         .         . 
S.G.  of  juice        .         .         .         . 

.     -0345 
.    -II73 
.     -1786 
.    I  -0356 

In  this  analysis  neither  the  water  nor  the  woody  fibre  was 
estimated  separately. 


[193 


PART   VI 

ANALYSIS  AND    VALUATION  OF 
MANURES 

193.  In  commerce  certain  constituents  of  the  substances 
dealt  with  are  valuable ;  others  are  of  no  value.  Hence  'a 
commercial  analysis — i.e.^  one  which  shall  indicate  the  value  of 
a  substance — will  only  estimate  the  valuable  parts.  Take,  for 
instance,  the  analysis  of  a  superphosphate.  Supposing  that  we 
wished  to  make  a  complete  investigation  of  the  substances 
contained  therein,  we  should  estimate  the  amounts  of  lime, 
alumina,  oxide  of  iron,  sulphuric  acid,  phosphoric  acid,  and  the 
different  alkalis,  both  in  the  soluble  and  insoluble  state ;  also 
the  amounts  of  moisture,  organic  matter,  and  siliceous  matter 
which  it  contains.  In  scientific  investigations  this  is,  of  course, 
often  necessary.  The  agriculturist,  however,  who  simply  wishes 
to  know  whether  he  has  got  value  for  his  money  or  not,  or 
the  manufacturer  who  wishes  to  value  his  manure,  does  not 
want  any  such  complex  knowledge.  In  many  cases  nothing 
is  required  but  the  percentage  of  soluble  phosphoric  acid,^ 
and  even  when  a  so-called  '  full '  analysis  is  asked  for  the 
only  constituents  needed  are  those  which  are  tabulated  on 
page  143. 

The  methods  described  in  this  chapter  are  strictly  com- 
mercial ones,  and  will  enable  a  student  who  has  not  time  to  go 

'  See  notes  on  valuation,  paragraphs  259-262. 


194,  195]       Analysis  and  Valuation  of  Manures        121 

through  a  full  course  of  analytical  chemistry  to  do  all  the  work 
which  is  ordinarily  necessary  in  an  agricultural  laboratory. 


ANALYSIS   OF   MINERAL   PHOSPHATES 

194.  Moisture. — The  moisture  given  off  at  100°  C.  is 
very  small  and  of  no  importance,  and  it  is  usual  to  estimate  it 
together  with  the  combined  water  and  organic  matter.  If, 
however,  it  should  be  required,  it  may  be  found  by  weighing 
out  about  2  grams  of  the  sample  in  a  porcelain  capsule,  and 
heating  in  the  steam  oven  until  it  ceases  to  lose  weight.  The 
loss  is  the  moisture. 

195.  Combined  Water  and  Organic  Matter.— The 
portion  used  for  the  estimation  of  moisture  is  emptied  into  a 
weighed  platinum  dish,  heated  over  an  Argand  at  the  highest 
temperature  procurable  without  allowing  the  flame  to  touch 
the  platinum.  After  about  an  hour  the  dish  is  placed  in  a 
Fletcher  muffle  furnace  (see  fig.  17),  and  kept  at  a  bright 
yellow  heat  for  twenty  minutes.  At  the  end  of  this  time  the 
gas  is  turned  off,  and  the  open  muffle  allowed  to  cool  to  a  dull 
red.  The  dish  is  then  removed  to  a  desiccator  and,  when 
cool,  weighed.  The  loss  of  weight  gives  the  sum  of  the  com- 
bined water,  the  organic  matter,  and  the  carbonic  anhydride. 

If  in  the  subsequent  analysis  it  should  be  noticed  that  the 
mineral  effervesces  on  the  addition  of  hydrochloric  acid,  the 
CO2  may  be  estimated  by  one  of  the  methods  described  in 
paragraphs  48-56.  The  amount  of  CO2  is,  however,  not  of 
much  consequence  to  the  manure  manufacturer  (see  page  155), 
and  very  often  a  fairly  accurate  idea  of  it  may  be  obtained  from 
the  quantities  of  lime  and  phosphoric  acid  present,  the  excess 
of  lime  over  the  phosphoric  acid  being  considered  as  CaCOg. 
This  method  of  calculation  is  of  course  impossible  in  the  case 
of  apatites. 


22  Analysis  and  Valuation  of  Manures 


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196,  197]  Method  of  Analysis  123 

METHOD   OF   ANALYSIS 

196.  The  method  followed  in  the  complete  analysis  of  a 
mineral  phosphate  may  be  seen  at  a  glance  from  the  table  on 
page  122.  A  word  or  two,  however,  should  be  said  concerning 
the  principles  involved.  The  determination  of  phosphoric  acid 
in  manures  is  always  rendered  difficult  by  the  presence  of  lime, 
alumina,  and  oxide  of  iron.  At  one  time  analysts  were  content 
to  dissolve  the  phosphate  in  hydrochloric  acid  and  make 
alkaline  with  ammonia.  This  gave  a  precipitate  of  mixed 
phosphates  of  iron,  aluminium,  and  calcium  which  was  weighed 
as  'total  phosphates.'  In  the  method  described  below,  ad- 
vantage is  taken  of  the  fact  that  the  phosphates  of  iron  and 
aluminimn  are  not  precipitated  by  ammonia  in  the  presence  of 
ammonium  citrate.  The  mixed  phosphates  may  thus  be  kept 
in  solution  by  a  mixture  of  ammonium  citrate  and  acetic  acid. 
Ammonium  oxalate  will  completely  precipitate  the  lime  from 
this  solution  in  the  form  of  calcium  oxalate.  After  this  pre- 
cipitation the  filtrate  may  be  rendered  alkaline  without  causing 
any  further  precipitate,  and  the  phosphoric  acid  may  be  deter- 
mined by  magnesia  mixture  as  described  on  page  27.  Each 
process  is  described  in  detail  in  the  sequel. 

197.  Estimation  of  Sand  and  Siliceous  Matter.— 
Weigh  out  about  2  grams  of  the  powdered  mineral,  transfer 
to  a  4-0Z.  wide-mouthed  beaker,  removing  the  last  traces  of 
powder  from  the  watch  glass  with  the  smallest  possible  quantity 
of  hot  water.  Add  10  c.c.  of  dilute  hydrochloric  acid,  and  cover 
with  a  watch  glass.  If  any  carbonates  be  present,  as  is  nearly 
always  the  case,  the  beaker  must  be  placed  on  top  of  the  steam 
oven  until  all  effervescence  ceases.  Add  20  c.c.  of  strong  HCl 
and  evaporate  down  to  dryness  on  the  water  bath,  driving  oft 
the  last  traces  of  moisture  on  the  sand  bath.  Allow  the  beaker 
to  cool,  then  add  5  c.c.  of  strong  HCl,  which  must  be  shaken 


124        Analysis  and  Valuation  of  Manures       [198,  199 

gently  round  the  beaker  until  all  the  substance  has  been 
moistened  with  it.  Warm  for  a  few  minutes  on  the  water  bath, 
then  add  about  20  c.c.  of  dilute  HCl  and  allow  to  digest  for  ten 
minutes.  Filter  off,  and  wash  with  hot  water  until  the  washings 
are  no  longer  acid  to  litmus  paper.  Transfer  the  filter  paper, 
without  drying,  to  a  weighed  platinum  dish.  Heat  over  an 
Argand  turned  down  very  low,  keeping  the  dish  covered  with 
a  square  of  platinum  foil.  When  the  paper  is  dry,  turn  up  the 
flame  so  as  just  to  char  the  paper.  As  soon  as  fumes  cease  to 
come  off,  turn  up  the  Argand  to  its  full  power  until  the  paper 
is  completely  burned.  Cool  in  a  desiccator,  and  weigh.  Sub- 
tract the  weight  of  the  dish  and  filter  ash.  Calculate  the 
percentage  of  the  residue,  and  enter  it  as  sand  and  insoluble 
silicates. 

198.  Lime. — To  the  filtrate  from  the  sand  add  ammonia 
until  a  precipitate  is  formed.  Dissolve  this  by  adding  2  grams 
of  citric  acid.  ^  If  the  precipitate  all  dissolves,  add  ammonia 
until  it  reappears,  and  strong  acetic  acid  until  it  goes  again. 
If  it  does  not  dissolve,  the  ammonia  may  be  omitted.  By  going 
through  these  operations  it  will  be  ensured  that  sufficient 
ammonia  is  present  to  convert  the  whole  of  the  citric  and  a 
portion  of  the  acetic  acid  into  ammonium  salts.  Raise  to  a 
boil,  add  2  grams  of  solid  ammonium  oxalate,  and  estimate  the 
lime  exactly  as  described  in  paragraphs  42-45.  The  reason 
for  adding  citric  acid  is  that  ammonium  citrate  prevents  the 
precipitation  of  phosphates  of  iron  and  aluminium. 

199.  Phosphoric  Acid. — Allow  the  filtrate  from  the  lime, 
which  should  not  exceed  200  c.c,  to  cool,  or  cool  it  by  placing 
the  beaker  in  a  vessel  through  which  passes  a  stream  of  cold 
water.     Then  add  50  c.c.  of  strong  ammonia  and  40  c.c.  of 

'  Citric  acid  sometimes  contains  insoluble  matter.  It  is,  therefore, 
better  to  dissolve  the  2  grams  of  acid  in  water,  and  filter,  if  necessary, 
before  adding  to  the  liquid. 


200]  Method  of  Analysis  125 

magnesium  chloride  mixture  (see  page  26),  stirring  vigorously 
all  the  while.  Allow  the  beaker  to  stand  two  hours,  stirring 
occasionally.  At  the  end  of  this  time  decant  the  liquid  off 
through  a  filter  paper.  When  as  much  of  the  liquid  has  been 
removed  as  possible  without  getting  the  precipitate  on  to  the 
filter,  remove  the  filtrate  beaker,  and  place  the  one  containing 
the  precipitate  under  the  funnel.  Wash  the  filter  paper  with 
dilute  hydrochloric  acid  until  the  washings  are  sufficient  to 
dissolve  the  precipitate  in  the  beaker  below.  Then  give  the 
paper  one  wash  with  dilute  ammonia.  Where  the  ammonia 
touches  the  liquid  in  the  beaker  it  will  give  a  white  precipitate. 
Complete  the  precipitation  by  adding  strong  ammonia  until 
strongly  ammoniacal.  (The  strong  ammonia  should  form  a 
quarter  of  the  whole  bulk.)  Allow  to  stand,  with  frequent 
stirrings,  for  half-an-hour,  then  filter  through  the  same  paper  as 
before.  Wash,  ignite,  and  weigh  exactly  as  in  paragraphs  39 
and  40. 

200.  Corrections  for  Solubility.— It  is  unfortunate  that 
phosphoric  acid,  which  is  so  important  a  constituent  of  manures, 
should  be  one  of  the  most  difficult  to  estimate  accurately.  If 
the  above  instructions  be  followed  out  carefully,  the  ammonium 
oxalate  and  the  citric  acid  being  weighed  out  before  adding  to 
the  solution,  then  a  result  will  be  obtained  which  is  considerably 
below  the  truth.  Several  circumstances  combine  to  bring  this 
about.  In  the  first  place,  Mg2(NH4)2(P04)2  is  slightly  soluble 
in  water  even  when  it  contains  a  large  quantity  of  ammonia. 
Ammonium  chloride  and  ammonium  oxalate  increase  the 
solvent  power  of  the  liquid,  as  also  do  citrates  of  iron  and 
aluminium.  Ammonium  citrate  does  not  seem  to  have  very 
much  influence,  except  that  it  makes  the  precipitation  much 
slower.  On  the  other  hand,  MgCl2  decreases  the  solubility  of 
the  precipitate,  but  should  large  excess  be  used  various  im- 
purities, including  magnesia  and  magnesium  oxalate,  occur  in 


126  Analysts  and  Valuation  of  Manures  [201 

the  precipitate.  The  second  precipitation  is  used  on  this 
account. 

Under  these  circumstances  it  is  necessary  to  make  an 
allowance  for  solubility.  The  matter  was  very  thoroughly  in- 
vestigated by  the  late  Dr.  Augustus  Voelcker,  who  considered 
that  when  two  grams  of  substance  are  taken  and  the  citrate 
process  is  used  as  described  above,  the  percentage  of  P2O.5 
found  is  "33  below  the  truth.  This  is  probably  the  best  addi- 
tion to  make,  and  it  is  used  in  all  analyses  throughout  this 
book  where  any  addition  is  made.  Any  exceptions  are  notified 
in  the  text. 

In  methods  where  neither  citrates  nor  oxalates  are  present 
in  the  solution  (see  paragraphs  207,  208,  237),  Fresenius' 
allowance  of  i  milligram  of  Mg2P207  for  every  54  c.c.  of  liquid 
in  the  filtrate  may  be  used. 

201.  Iron  and  Aluminium.— This  estimation  is  not 
always  performed,  as  a  very  shrewd  idea  of  the  quantity  of 
these  substances  present  may  be  obtained  by  adding  up  the 
results  of  other  determinations  and  subtracting  their  sum  from 
100.  It  is,  however,  of  considerable  importance  in  manure 
works  where  the  '  mineral  phosphate '  is  to  be  converted  into 
'superphosphate.'  The  amount  of  H2SO4  which  will  be 
needed  for  this  work  varies  considerably  with  the  amount  of 
Fe203  and  AI2O3  present,  as  will  be  readily  seen  by  comparing 
the  two  equations : 

Ca3(POj2  +  2H2SO,  =  2CaS04  +  CaH.lPO,)^  +  sH^O  ; 
Ca3(PO^)2  +  AI2O3  +  5H2SO,  =  2CaS0,  +  Al2{SO,)3  +  CaH,(PO,),. 

Should  insufficient  acid  be  used,  some  of  the  soluble  phosphate 
will  be  rendered  insoluble,  thus  : 

CaH4(P0  J,  -H  AI2O3  +  H2SO4  =  CaSO,  +  A1,{P04)2  -h  3H,0. 

The  best  method  at  present  in  use  was  originally  invented 
by  Glaser,  but  has  gone  through  many  modifications  as  to 
details.     It  is  known  as  the  Glaser,  or  alcohol,  method.     Like 


202]  Method  of  Analysis  127 

many  other  of  the  special  methods  used  in  agricultural  analysis, 
or  indeed  in  any  other  branch  of  technical  analysis,  it  is  very 
necessary  that  the  instructions  as  to  quantities,  &c.,  should  be 
exactly  followed  out. 

202.  Weigh  out  2-5  grams  of  the  finely  powdered  mineral 
on  a  watch  glass.  Transfer  to  a  beaker,  washing  the  glass  with 
a  little  hot  water.  Add  a  little  dilute  HCl,  and  digest  on  top 
of  the  water  oven  until  all  effervescence  ceases.  Now  add  20 
to  30  c.c.  of  pure  strong  HCl,  and  evaporate  thoroughly  to  dry- 
ness on  the  water  bath.  This  will  get  rid  of  any  fluorine  which 
may  be  present.  When  dry  dissolve  in  about  10  c.c.  of  dilute 
HCl  (one  part  of  strong  acid  to  four  of  water),  allowing  it  to 
digest  until  nothing  is  left  undissolved  excepting  the  siliceous 
matter.  This  operation  may  be  materially  assisted  by  break- 
ing up  any  lumps  with  a  stirring  rod.  Pour  the  liquid  into  a 
250-c.c.  flask,  washing  the  residue  into  the  flask  with  the 
smallest  possible  quantity  of  water— 25  c.c.  should  be  sufficient. 
Measure  out  10  c.c,  of  pure  strong  H2SO4  with  a  pipette,  and 
run  it  into  the  flask.  A  thick  precipitate  of  CaSOj  will  be 
formed.  Shake  the  flask  gently  in  a  rotatory  manner  until  the 
liquids  are  thoroughly  mixed,  and  allow  to  cool.  Fill  up  to  the 
250-c.c.  mark  with  95  per  cent,  alcohol.  On  allowing  this 
to  stand,  the  liquid  will  be  found  to  contract.  Shake  it  up 
well ;  allow  it  to  cool,  and  make  up  to  the  mark  again  with 
alcohol  and  shake.  Place  a  funnel  with  a  dry  filter  paper  in 
the  mouth  of  a  200-c.c.  flask,  and  filter  off"  the  liquid  until 
200  c.c.  have  been  collected.  Evaporate  these  200  c.c.  (which 
contain  the  Fe  and  Al  in  2  grams  of  the  mineral)  in  a  large 
platinum  dish.  This  may  be  started  over  a  water  bath,  but  as 
soon  as  most  of  the  alcohol  has  evaporated  it  must  be  placed  on 
a  pipeclay  triangle  over  a  rose  burner.  Heat  until  the  sulphuric 
acid  begins  to  fume  strongly.  This  will  thoroughly  char  any 
organic  matter  which  might  otherwise  interfere  with  subse- 
quent operations.     Allow  the  dish  to  cool,  then  wash  it  out 


128  Analysis  and  Valuation  of  Manures  [203 

into  a  tall  beaker,  diluting  to  about  50  c.c.  Add  good  excess 
of  bromine  and  boil  to  oxidise  the  carbonaceous  matter. 
When  the  bromine  has  all  gone,  make  just  alkaline  with  am- 
monia. Add  about  5  grams  of  pure  ammonium  acetate,  then 
make  just  acid  with  acetic  acid.  Bring  the  liquid  up  to  a  boil, 
then  cool  quickly,  and  filter.  Wash  with  hot  water  containing  a 
little  ammonium  nitrate.  This  precipitate  contains  the  normal 
phosphates  of  iron  and  aluminium.  (Some  analysts  weigh  this 
precipitate,  and  consider  the  FcsOa  and  AI2O3  to  constitute 
half  its  weight.  This,  however,  leads  to  faulty  results.)  Dis- 
solve the  precipitate  in  dilute  nitric  acid,  collecting  the  liquid 
in  a  4-0Z.  conical  flask  fitted  with  an  india-rubber  stopper.  Add 
about  5  c.c.  of  strong  NH4NO3  solution  ;  heat  nearly  to  boiling 
(85°  C.  is  the  correct  temperature).  Add  25  c.c.  of  ammonium 
molybdate  solution.  Cork  up  the  flask,  and  shake  vigorously 
for  about  three  minutes.  Filter  off  the  yellow  precipitate, 
which  will  contain  all  the  phosphoric  acid.  Make  the  filtrate 
alkaline  with  ammonia,  boil,  and  filter.  The  precipitate  will 
consist  of  the  hydrates  of  iron  and  alumina,  slightly  contami- 
nated with  molybdic  acid.  To  remove  this,  dissolve  in  HCl 
and  reprecipitate  with  ammonia.  Wash  well,  dry,  ignite,  and 
weigh  as  Fe203  +  Al203.  To  separate  these  two,  dissolve 
in  strong  HCl.^  Make  up  to  250  c.c.  with  water.  Mix  the 
solution  thoroughly,  and  determine  the  iron  as  described  in 
paragraphs  75-77- 

203.  Calculation  of  'R^SvXtS.— Phosphoric  acid.  This 
is  calculated  as  P2O5  from  the  Mg2P207.  It  is  always  best  in 
calculating  results  to  begin  by  finding  the  percentage  which  the 
precipitate  is  of  the  substance  taken.  Thus  we  should  begin 
by  multiplying  the  weight  of  Mg2P207  by  100,  and  dividing  it 
by  the  weight  of  mineral   phosphate   which  has  been   used. 

'  It  will  often  be  found  that  this  precipitate,  after  ignition,  is  very 
insoluble  in  HCl.  Some  analysts  always  use  HjSO^,  which  acts  more 
rapidly. 


204] 


Method  of  Analysis 


i2g 


This  will  be  found  to  simplify  further  calculations  considerably. 
The  percentage  so  found  may  be  calculated  into  P2O5  by  the 
proportion 

Mol.  wt.  of  Mg,P,0,  :  Mol.  wt.  of  F,0,  :  :  o^  of  Mg^P.O,  :  o^  of  P.,0,. 

From  the  percentage  of  P2O5  so  found  that  of  the  CagPgOg  is 
calculated. 

These  calculations,  and  most  others,  are  very  much  simplified 
by  using  factors,  of  which  a  list  is  given  in  the  appendix. 
Thus,  the  percentage  of  Mg2P207  x  '64  =  the  percentage  of 
P2O5.  To  this  the  addition  of  -33  must  be  made,  and  the 
result  multiplied  by  155  and  divided  by  71,  or  simply  multiplied 
by  2'i83i,  which  gives  the  percentage  of  Ca3P208.  In  future 
the  simplest  means  of  calculation  is  always  given,  and  should 
be  verified  by  using  the  ordinary  method. 

jLt'me.  The  substance  weighed  is  CaCOg.  Find  the  per- 
centage and  multiply  by  '56  ;  this  gives  the  percentage  of  CaO. 
Subtract  the  P2O5  from  the  CagPaOg.  This  gives  the  CaO 
combined  with  the  P2O5.  To  find  the  amount  of  CaO  as 
carbonate,  subtract  the  amount  combined  with  P2O5  from  the 
total,  and  divide  by  -56.  Should  the  CO2  be  determined 
separately,  the  excess  of  CaO  is  entered  as  such. 

204.  Mode  of  Entry  : 


Cam- 

bridge 

coprolites 

Spanish 
phosphor- 
ite 

Canadian 
apatite 

West 

Indian 

phosphate 

German 
phosphate 

Moisture              \ 
Combined  water  I     . 
Organic  matter    ] 
Calcic  phosphate 
Calcic  carbonate 
Oxide  of  iron    . 
Alumina  . 

Magnesia,  alkalis,  &c. 
Silicates   . 

4-04 

58-09 
21-12 

2-i8 

2-05 

4-33 
8-19 

•16 

85-33 
6-89 

I     1-66 
J 

5-96 

•II 

82-25 

■    13-35 

4-29 

5'9i 

}     5-46 

68-07 

I -60 

■  17 '94 
I -02 

■      -25 

83-21 
6-25 

10-20 

-09 

100 -oo 

loo-oo 

100-00  1  loo-oo 

100-00 

130        Analysis  and  Valuation  of  Manures      [205,206 

ANALYSIS   OF   BASIC   SLAG 

205.  A.  The  moisture  is  estimated  as  usual  in  2  grams  of  sub- 
stance. It  contains  neither  organic  matter  nor  combined  water, 
as  is  to  be  expected  from  a  substance  which  is  produced  at  the 
high  temperature  of  the  Bessemer  converter. 

205.  B.  Lime  and  Phosphoric  Acid.— The  phosphate 
of  lime  which  is  contained  in  this  substance  has  the  formula 
Ca4P209,  and  its  constitution  may  be  understood  by  consider- 
ing it  to  be  a  compound  of  Ca3(P04)2  and  CaO.  Thus  the 
four  phosphates  of  lime  met  with  in  manures  are 

CaO.P2O5.2H2O  or  CaH4P208,  soluble  phosphate  ; 
2CaO.P2O5.H2O  or  Ca2H2P20g,  reverted  phosphate  ; 
3CaO.P205  or  Ca3P208,  tricalcic  phosphate  ; 
4CaO.P205  or  Ca.iP209,  basic  phosphate. 

Four  methods  are  given  here  for  the  analysis  of  basic  slag. 

206.  The  first  method  of  analysis  is  similar  to  that  of 
mineral  phosphates  with  the  following  differences :  A  mixture 
of  nitric  and  hydrochloric  acids,  equal  parts,  is  used  to  dis- 
solve the  substance.  This  is  in  order  to  oxidise  the  large 
amount  of  ferrous  oxide  present. 

Eight  grams  of  citric  acid,  and  a  consequent  increase  in  the 
amount  of  ammonia,  are  used  to  keep  the  oxide  of  iron  in 
solution.  Even  then  the  magnesium  ammonium  phosphate  pre- 
cipitate will  contain  a  trace  of  iron,  and  this  must  be  removed 
by  adding  '5  gram  of  citric  acid  before  reprecipitating.  For 
the  precipitation  of  this  lime  3  to  4  grams  of  ammonium  oxalate 
must  be  used,  and  the  precipitate  redissolved  and  reprecipi- 
tated. 

The  extra  amount  of  citric  acid  makes  the  precipitation  of 
the  Mg2(NH4)2(P04)2  somewhat  slower.  The  solution  must 
therefore  be  allowed  to  stand,  with  frequent  stirring,  for  two  and 


207,  208]  Analysis  of  Basic  Slag  131 

a-half  hours.     The  reprecipitation  in  the  same  way  will  occupy 
an  hour. 

207.  Second  method,  used  for  estimation  of  phosphoric 
acid  only.  Should  the  percentage  of  lime  not  be  required,  the 
weighed  portion  of  slag  (i  gram)  may  be  dissolved  in  25  c.c.  of 
strong  H2SO4.  This  is  done  in  a  flask  on  a  sand  bath,  and  the 
liquid  heated  until  it  fumes  strongly.  It  is  then  allowed  to  cool 
and  is  poured  into  a  beaker  containing  75  c.c.  of  water.  The 
flask  is  rinsed  out  two  or  three  times  with  water.  The  muddy 
liquid  is  allowed  to  settle,  and  filtered.  The  precipitate  is  well 
washed,  8  grams  of  citric  acid  and  excess  of  ammonia  are  added, 
and  the  liquid  cooled.  The  phosphoric  acid  is  precipitated  as 
before  by  25  c.c.  of  MgCl2  mixture  and  excess  of  strong  am- 
monia. This  method  is  not  so  reliable  as  the  last,  as  the 
calcium  citrate  has  a  solvent  action  on  the  precipitate,  whilst, 
on  the  other  hand,  the  sulphuric  acid  present  tends  to  throw 
down  a  basic  magnesium  sulphate  along  with  the  phosphate 
precipitate. 

208.  Rapid  method  for  the  estimation  of  phosphoric  acid. 
For  this  estimation  it  is  necessary  to  prepare  two  solutions, 
one  of  ammonium  nitrate,  the  other  of  ammonium  molybdate. 

Ammonium  Nitrate.  Dissolve  100  grams  in  90  c.c.  of  hot 
water ;  when  cold,  make  up  to  165  c.c.  with  distilled  water. 

Ammonium  Molybdate.  Measure  100  c.c.  of  water  into  a 
large  flask.  Add  50  grams  of  molybdic  acid,  then  100  c.c.  of 
•880  ammonia.  Stir  until  dissolved.  Pour  the  solution  quickly 
into  a  large  stoneware  jug  containing  720  c.c.  of  cold  nitric 
acid  (S.G.  1*20),  stirring  well  whilst  adding.  Allow  to  stand 
over  night,  and  filter. 

Weigh  out  exactly  *5  gram  of  the  sample.  Transfer  to  a 
4-0Z.  wide-mouthed  beaker,  and  add  8  c.c.  of  strong  pure  HCl. 
Evaporate  to  dryness  on  the  water  bath,  finishing  on  the  sand 
bath.     Allow  to  cool  j  then  moisten  with  8  c.c.  of  pure  HCl, 


132  Analysis  and  Valuation  of  Manures  [209 

and  add  12  c.c.  of  water.  Evaporate  on  the  water  bath  until 
the  liquid  has  diminished  to  about  half  its  original  bulk.  Filter 
into  a  250-c.c.  flask.  Wash  with  water  slightly  acidulated  with 
HCl.  Make  up  to  250  c.c.  with  distilled  H2O.  After  mixing 
take  25  c.c.  and  transfer  to  a  5-oz.  conical  flask  fitted  with  a 
caoutchouc  stopper.  Add  18  c.c.  of  the  ammonium  nitrate 
solution.  Heat  to  85°  C.  Add  20  c.c.  of  ammonium  molyb- 
date  solution,  cork  the  flask,  and  shake  vigorously  for  one 
minute.  Filter  through  a  very  smooth  filter  paper.  Wash 
three  times  with  dilute  HNO3  (1-20).  Then  remove  the 
paper,  and  wash  all  the  yellow  precipitate  from  the  paper  into 
a  weighed  platinum  dish.  Evaporate  to  dryness  on  the  water 
bath.  Finally,  dry  in  the  steam  oven,  cool,  and  weigh,  llie 
weight  of  the  precipitate  x  74*66  =  percentage  of  P2O5. 

209.  Molybdate  and  magnesia  method.  This  is  per- 
haps the  most  reliable  method  for  the  estimation  of  phosphoric 
acid,  and  certainly  the  one  most  generally  applicable. 

Weigh  out  I  gram  of  the  sample.  Dissolve  in  a  mixture  of 
15  C.C.  hydrochloric  acid  (S.G.  i'i6)  and  15  c.c.  nitric  acid 
(S.G.  1*42),  evaporating  to  dryness  to  separate  the  silica.  Add 
20  c.c.  hydrochloric  acid  (S.G.  i"i6),  and  evaporate  until  it 
only  occupies  about  half  the  original  bulk.  Add  20  c.c.  boiling 
water,  and  filter.  Collect  the  filtrate  in  a  250-c.c.  flask.  Make 
up  to  the  250-c.c.  mark  with  water.  Take  50  c.c.  of  this  liquid 
with  a  pipette,  and  introduce  it  into  an  8-oz.  conical  flask 
fitted  with  an  india-rubber  cork.  Add  ammonia  until  a  per- 
manent precipitate  is  formed.  Dissolve  this  in  the  smallest 
possible  quantity  of  nitric  acid.  Heat  to  85°  C.  Add  200  c.c. 
ammonium  molybdate  solution  (see  paragraph  208).  Cork 
the  flask,  and  shake  vigorously  for  five  minutes.  Allow  the 
precipitate  to  settle,  then  filter.  Wash  once  by  decantation, 
then  two  or  three  times  on  the  filter  paper,  using  i  in  20  nitric 
acid.     This  precipitate   will   contain  all  the  phosphoric  acid. 


210,  211] 


Analysis  of  Basic  Slag 


133 


Dissolve  it  in  dilute  ammonia,  and  wash  the  filter  well  with 
hot  water,  collecting  the  solution  and  washings  in  an  8-oz. 
beaker.  Neutralise  the  liquid  with  HCl,  then  add  20  ex.  of 
magnesia  mixture  and  20  c.c.  of  strong  ammonia.  Stir  well, 
and  allow  to  stand  for  an  hour  and  a-half.  Filter,  wash  with 
ammonia,  dry,  ignite,  and  weigh  as  Mg2P207. 

210.  Calculation. — In  the  case  of  basic  slag  the  calcula- 
tion is  simple,  as  nothing  is  required  beyond  the  percentages 
of  lime,  phosphoric  acid  (P2O5),  and  silica.  The  difference 
between  the  sum  of  these  percentages  and  100  is  put  down  as 
oxide  of  iron,  &c.  It  consists  of  MgO,  AI2O3,  FeO,  V2O3,  and 
SO,. 

The  following  are  a  few  typical  results  : 


I 

II 

III 

IV 

Moisture . 
Lime,  CaO 
♦Phosphoric  acid 
Ferrous  oxide,  &c.    . 
Silica 

46-00 

15-82 

29-87 

8-31 

43-48 
11-46 
29-44 
15-62 

0-13 
32-42 
18-44 
39-46 

9-55 

46-33 
17-95 
25-59 

10-13 

loo-oo 

loo-oo 

lOO-OO 

100-00 

♦Equal  to  CagCPOJ,  . 

34-53 

25-02 

40-26         39-19 

211.  Estimation  of  Fineness.— The  value  of  basic 
slag  is  greatly  increased  by  being  well  ground ;  therefore  it  is 
often  necessary  to  test  its  fineness.  This  is  readily  done  by 
weighing  out  10  grams  into  a  small  wire  sieve  having  100 
meshes  to  the  linear  inch.  It  is  ordinarily  said  that  the  whole 
of  the  10  grams  should  pass  through  this,  but  in  practice  it  is 
generally  found  that  from  70  to  95  per  cent,  passes  through. 
The  sieve  is  shaken  until  as  much  has  been  passed  through  as 
will  go,  and  this  is  collected  and  weighed. 


134        Analysis  and  Valuation  of  Manures       [2 12-214 

ANALYSIS  OF   BONE  MEAL 

212.  Moisture  and  Organic  Matter.— Estimated  as  in 
mineral  phosphates  (see  paragraphs  194  and  195). 

213.  Sand. — About  2  grams  of  the  substance  are 
weighed  out  and  dissolved  in  hydrochloric  acid,  with  all  the 
precautions  described  in  paragraph  10.  Then,  instead  of 
boiling  down  to  dryness,  the  liquid  containing  the  sand  and 
organic  matter  is  treated  with  ammonia,  citric  acid,  and  acetic 
acid,  raised  to  boiling-point,  and  the  Hme  thrown  down  with 
ammonium  oxalate,  every  detail  as  to  quantities  being  carried 
out  as  described  in  paragraphs  198  and  199.  The  precipitate 
is  collected  on  a  filter,  washed,  and  finally  burned,  as  though 
it  were  calcium  oxalate.  The  organic  matter  will  be  oxidised, 
and  the  precipitate  may  be  weighed  as  CaCOg  +  sand.  After 
weighing,  the  dish  is  emptied  into  a  beaker,  and  the  CaCOa 
dissolved  in  dilute  HCl.  The  sand  may  then  be  filtered  off, 
washed,  and  weighed,  as  in  paragraph  197. 

214.  The  reason  for  this  mode  of  procedure  is  twofold  : 
Firstly.     If  the  acid   liquid  containing   the  phosphate   of 

lime,  &c.,  in  solution  and  the  sand  in  suspension  be  filtered  at 
once,  the  gelatinous  nature  of  the  organic  matter  in  the  liquid 
will  often  render  filtration  very  slow.  The  precipitate  of  cal- 
cium oxalate  carries  down  the  gelatinous  matter  with  it,  and 
thus,  after  precipitation  with  ammonium  oxalate,  the  liquid 
passes  through  the  paper  quite  easily. 

Secondly.  Since  the  precipitation  of  phosphoric  acid  with 
magnesia  mixture  takes  some  considerable  time,  it  is  advisable 
to  get  it  thrown  down  as  soon  as  possible.  By  precipitating 
lime  and  sand  together  we  get  the  liquid  for  precipitation  with 
magnesia  mixture  at  once,  and  thus  we  are  enabled  to  go  on 
with  the  lime  and  sand  estimation  whilst  the  phosphoric  pre- 
cipitate is  forming,  using  40  c.c.  MgCl2  mixture. 


215-217] 


Analysis  of  Bone  Meal 


135 


215.  Phosphoric  Acid. — This  is  estimated  in  the 
filtrate  from  the  lime  and  sand,  exactly  as  described  in  para- 
graph 199  for  mineral  phosphates. 

216.  Nitrogen. — Two  grams  are  used  for  this  esti- 
mation, which  may  be  done  by  either  of  the  two  methods 
described  in  paragraphs  86-95. 

217.  Calculation  of  Results.— From  the  MggPgO; 
calculate  the  percentages  of  P2O5  and  CaaPaOg.  From  the 
CaCOa  calculate  the  percentage  of  CaO.  Find  the  excess  of 
CaO  as  in  mineral  phosphate  analysis. 

The  excess  of  CaO  is  used  as  a  check  on  the  accuracy  of 
the  rest  of  the  analysis,  which  is  put  out  in  this  form  : 


Raw  bones 

Boiled  bones 

Bone  ash 

Bone  flour 

Moisture . 
♦Organic  matter 

Phosphate  of  lime     . 
fCarbonate  of  lime,  &c. 

Sand  ... 

8-29 

27-18 

48-92 

7-71 

7-90 

9-65 

16-95 

62-15 

8-56 

2-69 

11-99 
2-77 

74-55 
9-48 

I -21 

8-45 

17-29 

63-99 

8-97 

1-30 

icx)-oo 

100-00 

loo-oo 

lOO'OO 

♦Containing  nitrogen  . 
Equal  to  ammonia    . 
f  Containing  lime 

4-10            I-I8 
4-98         1-43 

3-31              4-02 

I -61 

1-35 
1-64 

4-57 

It  is  not  usual  to  state  the  excess  of  lime,  but  it  is  always 
well  to  calculate  it  out.  It  should  amount  (in  bones)  to  a  little 
less  than  half  the  '  CaCOg,  &c.,'  which  is  the  difference  between 
the  sum  of  the  other  percentages  and  100. 

The  percentage  of  nitrogen,  multiplied  by  17  and  divided 
by  14,  gives  the  percentage  of  ammonia. 

The  analysis  of  bone  ash  is  exactly  similar  to  that  of  bone 
meal,  except  that  the  nitrogen  is  not  estimated. 


136        Analysis  and  Valuation  of  Manures       [218-220 


ANALYSIS   OF   GUANO 

218.  The  name  *  guano '  is  applied  to  such  a  large  assortment 
of  manures  that  no  one  method  can  be  described  applicable  to 
all.  Any  manure,  therefore,  bearing  the  simple  name  '  guano  ' 
should  be  tested  with  blue  litmus  paper.  If  it  give  a  decidedly 
acid  reaction,  it  must  be  analysed  by  the  method  given  for 
superphosphates.  If  not,  it  should  be  proceeded  with  in 
much  the  same  manner  as  bones,  except  that  the  organic 
matter  7nust  be  burned  off  before  the  lime  and  phosphoric  acid 
are  estimated. 

219.  Moisture. — When  a  Peruvian  guano  is  heated  to 
100°  C,  it  gives  off  not  only  moisture,  but  also  a  certain  amount 
of  ammonia.  For  ordinary  commercial  purposes  this  makes  very 
little  difference,  and  the  estimation  may  be  performed  in  the 
usual  way.  A  more  exact  method  is  as  follows  :  About  5  grams 
are  weighed  out  in  a  U  tube.  One  end  of  this  tube  is  connected 
with  a  small  wash  bottle,  containing  20  c.c.  of  seminormal 
acid,  in  such  a  manner  that  when  a  current  of  air  is  aspirated 
through  the  apparatus  it  passes  first  through  the  U  tube  and 
then  bubbles  through  the  acid.  The  lower  part  of  the  U  tube 
which  contains  the  guano  is  immersed  in  boiling  water,  and 
the  free  tube  of  the  wash  bottle  connected  with  an  air-pump  or 
aspirator.  In  this  manner  all  the  ammonia  which  is  liberated 
is  absorbed  by  the  acid.  When  the  U  tube  no  longer  loses 
weight  the  acid  is  titrated  with  quinquinormal  potash,  and 
from  this  the  NH3  which  has  been  absorbed  may  be  calcu- 
lated. The  loss  of  weight  sustained  by  the  guano  is  moisture 
plus  ammonia.  The  moisture  may  thus  be  calculated  by 
difference. 

220.  Sand,  Lime,  and  Phosphoric  Acid.— Weigh 
out  about  2  grams  of  guano  in  a  platinum  dish  and  burn  over 


221,  222]  Analysis  of  Guano  137 

an  Argand,  being  careful  not  to  exceed  a  dull-red  heat,  or 
some  of  the  alkaline  salt  will  fuse  and  render  the  mass  difficult 
to  remove  from  the  dish. 

The  ash  of  a  pure  guano  should  be  perfectly  white. 

Weigh  the  dish  and  guano  after  burning,  and  enter  the  loss 
as  organic  matter  plus  moisture. 

Transfer  the  residue  to  a  beaker,  washing  the  last  traces  off 
the  dish  with  a  little  dilute  HCl ;  dissolve  up  in  strong  HCl, 
and  proceed  as  in  the  case  of  mineral  phosphates  (see  para- 
graphs 198  and  199),  adding,  however,  only  i^  gram  of  ammo- 
nium oxalate. 

221.  Nitrogen. — The  guano  should  be  tested  for  nitrates 
thus  :  About  5  grams  of  guano  are  extracted  with  water ;  to 
the  filtered  solution  are  added  a  small  quantity  of  indigo  solu- 
tion and  strong  sulphuric  acid  equal  in  bulk  to  the  water  used. 
Bleaching  of  the  liquid  indicates  the  presence  of  nitrates. 

Should  nitrates  be  absent,  the  acid  method  may  be  used 
(see  paragraphs  90-95). 

Should  nitrates  be  present,  the  modified  method  described 
in  paragraph  99  must  be  used. 

The  ammonia  in  a  true  guano  should  be  about  a  quarter  of 
the  organic  matter. 

Ordinary  guanoes  do  not  contain  nitrates,  with  the  ex- 
ception of  Bats'  guano,  which  probably  contains  nitric  acid 
in  combination  with  lime.  The  name  'guano,'  however,  is 
so  popular  with  farmers  that  many  compound  artificial 
manures  are  sold  as  guano.  Hence  the  necessity  for  testing 
with  indigo. 

222.  Calculation. — On  calculating  out  the  quantities  ot 
CaO  and  P2O5  a  true  guano  will  show  an  excess  of  P2O5  over 
the  CaO.  Should  the  CaO  be  in  excess,  the  result  is  entered 
exacdy  like  that  of  bones.  Should  the  P2O5  be  in  excess,  there 
are  two  methods  in  use.     The  most  scientific  is  to  put  down  in 


138 


Analysis  and  Valuation  of  Manures 


[223 


order  the  percentages  of  moisture,  organic  matter,  P2O5,  CaO, 
difference  (alkalis,  &c.),  and  sand,  stating  as  footnotes  the  per- 
centage of  N  and  its  equivalent  of  ammonia,  and  also  the  equi- 
valent of  P2O5  in  CagPgOg.  The  more  common  method, 
however,  is  to  calculate  out  the  CagPsOg  equivalent  to  the  CaO 
present,  and  set  out  the  analysis  thus  : 


Peruvian 

Peruvian 

Patago- 
nian 

Meat 
guano 

Moisture        .... 

15-00 

9-71 

29-20 

9-60 

♦Organic  matter 

23-65 

40-19 

26-40 

50-85 

Ca3(P0,),      .... 

31-68 

19-00 

20 -44 

26-92 

fAlkalis,  &c.            ... 

23-02 

13-05 

7-36 

11-38 

Sand 

6-65 

18-05 

16-60 

1-25 

lOO'OO 

100-00 

100-00 

100-00 

♦Containing  nitrogen 

4-83 

8-45 

6-81 

5-94 

Equal  to  ammonia 

5-87 

10-26 

8-27 

7-22 

fContaining  P2O  5    . 

4-92 

-40 

•56 

4-87 

Equal  to  CajiPOJ., 

10-74 

-87 

1-22 

7-04 

Total  P2O5    .... 

19-43 

9-10 

9-92 

1 6 -20 

Equal  to  CajCPOJa 

42-42 

19-87 

21-66 

33-96 

A  Bats'  guano  contains  about  12  per  cent,  phosphate  of 
lime,  with  5  per  cent,  of  organic  nitrogen  and  4  per  cent,  of 
nitric  nitrogen. 

223.  Fish  Manure,  or  fish  guano,  is  analysed  exactly 
like  guano,  with  the  exception  that  the  oil  is  estimated.  This 
is  done  in  the  same  manner  as  the  oil  in  oil  cakes  (see  para- 
graphs 140,  141,  and  142).  The  oil  should  not  be  above  3  per 
cent.,  as  it  forms  a  protective  covering  and  prevents  the  manure 
from  rotting  in  the  ground. 


224-226]     Analysis  of  Superphosphate  of  Lime 


139 


ANALYSIS   OF   SUPERPHOSPHATE   OF  LIME 

224.  The  general  outline  of  the  method  may  be  seen  from 
the  following  table  : 


Treat  with  water.     Filter. 


Precipitate.  Transfer  to  a  plati- 
num capsule,  and  burn  off 
paper  and  organic  matter. 
Treat  with  dilute  HCl.     Fil- 


Precipitate. 
Weigh  as 
Sand. 


Filtrate.  Add 

ammonia  in  ex- 
cess, filter,  and 
weigh  precipi- 
tates as  insolu- 
ble phosphates. 


Filtrate.  Treat  with  citric  acid, 
ammonia,  and  acetic  acid.  Boil. 
Add  ammonium  oxalate.    Filter. 


Precipitate 
consists 
of       cal- 
cium oxa- 
late.   Re- 
ject. 


Filtrate.  Add  strong 
ammonia  and 

magnesia  mixture. 
Weigh  the  preci- 
pitate as  MgaP^Oj 
and  calculate 

from  this  the 
soluble  phospho- 
ric acid. 


225.  Moisture. — Weigh  out  2  grams  in  a  porcelain 
capsule,  heat  in  the  steam  oven  for  about  five  hours,  cool  in 
desiccator,  and  weigh  ;  return  to  oven  for  about  half-an-hour. 
Cool  and  weigh  again.     Repeat  until  weight  is  constant. 

226.  Organic  Matter. — The  organic  matter  in  a  mineral 
superphosphate  is  very  small,  but  in  one  made  from  bones 
it  is  considerable.  Should  the  analyst  require  to  know  the 
amount  exactly,  the  following  process  must  be  carried  out : 
Two  grams  are  weighed  out  into  a  platinum  crucible,  and  milk 
of  lime  is  added  until  the  mass  is  alkaline.  It  is  then  dried  in 
the  air  bath  at  150°  C.  until  its  weight  is  constant.  It  is  next 
ignited  on  the  Fletcher  muffle  furnace  for  twenty  minutes, 
cooled,  and  weighed.  The  difference  between  this  weight  and 
the  weight  after  drying  at  150°  C.  is  the  weight  of  organic 
matter  and   combined   water.      Should  the  amount  only  be 


140  Analysis  and   Valuation  of  Manures  [227 

required  approximately,  the  superphosphate,  after  drying, 
may  be  transferred  to  a  weighed  platinum  dish,  ignited  over  an 
Argand  in  a  draught  cupboard  until  it  has  lost  its  dark  colour, 
then  heated  over  the  blow-pipe  until  it  ceases  to  fume.  It  is 
then  cooled  in  a  desiccator  and  weighed.  The  loss  is  due  to 
organic  matter,  sulphuric  acid,  and  changes  in  the  composition 
of  the  phosphates.  In  almost  all  cases  the  loss  diie  to  sul- 
phuric acid  and  the  changes  in  the  phosphates  amounts  to  half 
the  weight  of  soluble  phosphate  calculated  as  CaPaOg.  If  this 
amount,  therefore,  be  subtracted  from  the  total  loss,  a  very 
close  approximation  to  the  amount  of  organic  matter  will  be 
obtained.^ 

227.  Soluble  Phosphoric  Acid.— A  portion  of  the 
powdery  sample  is  selected  as  described  in  the  chapter  on 
sampling,  Part  IV.,  paragraph  119,  and  placed  in  an  iron  mortar. 
It  is  banged  with  the  pestle  until  a  smooth,  pasty  mass  is 
obtained.  This  takes  two  or  three  minutes.  Of  course  it  may 
happen  that  a  very  dry  sample  has  been  obtained,  in  which 
case  it  will  not  become  pasty.  In  such  a  case  it  must  be 
remembered  that  the  object  of  triturating  in  an  iron  mortar  is  to 
break  down  all  hard  lumps  and  to  render  the  mass  as  homo- 
geneous as  possible.  When  the  mass  is  thoroughly  mixed,  a 
portion  is  taken  out  with  a  spatula.  It  takes  some  little  practice 
to  enable  the  operator  to  take  off  about  the  right  quantity,  but 

^  When  soluble   phosphate   of  lime  is  strongly  heated  with  calcium 
sulphate  the  following  reaction  takes  place  : 

CaH,(P04)2  4-  CaSO^  =  Ca2H,(P04)2  +  H^SO^, 

of  which  the  H2SO4  is  volatilised — i.e.,  one  molecule  of  CaH4(P04)2 
which  is  calculated  in  the  analytical  result  as  CaPgOg  [CaH4(P04)2  — 2H2O] 
will  liberate  one  molecule  of  1X2804.  Or,  in  figures,  198  parts  by  weight 
of  CaPjOg  will  liberate  98  parts  of  HjSO^.  Hence  the  change  in  the 
phosphates  and  loss  of  H2SO4  on  heating  a  superphosphate  amounts  to 
^,  or  about  half  the  weight  of  the  soluble  phosphate  calculated  as  CaPjOg. 


228]  Analysis  of  Superphosphate  of  Lime  141 

if  more  than  3  grams  or  less  than  i  gram  has  been  taken,  then 
another  portion  should  be  taken  from  the  mortar.  Two  grams 
should  be  the  quantity  used.  This  is  weighed  out  on  a  watch 
glass.  The  next  operation  is  to  mix  this  thoroughly  with  water. 
The  method  which  is  most  effective  is  somewhat  difficult 
to  describe,  though  in  reahty  very  simple.  A  beaker  about 
2\  inches  high  by  i^  inch  broad  is  taken,  and  the  weighed 
mass  of  '  super '  is  placed  in  it  by  means  of  a  stout  glass  rod 
3 1  inches  long.  The  portion  sticking  to  the  watch  glass 
is  washed  in  with  not  more  than  10  c.c.  of  water.  The 
substance  has  now  to  be  rubbed  round  the  beaker  with 
the  rod  very  rapidly  until  it  forms  with  the  water  a  thin  paste 
containing  no  clots.  In  doing  this  the  sides  of  the  beaker  will 
become  smeared  all  over  with  the  paste.  This  is  washed  to  the 
bottom  of  the  beaker  with  a  jet  of  cold  water,  and  the  liquid 
made  up  to  about  50  c.c.  It  is  then  allowed  to  stand  ten 
minutes,  when  it  will  have  settled  to  a  considerable  extent. 
The  liquid  is  decanted  through  a  filter  into  an  8-oz.  beaker. 
The  beaker  is  filled  up  again  to  the  same  level  and  decanted  off. 
This  is  repeated  with  cold  and  hot  water  until  all  the  soluble 
portion  is  extracted.  The  following  series  of  washings  should 
be  followed  exactly  : 

{a)  Stir  up  with  cold  water  50  c.c.  ; 
{b)  Fill  up  twice  with  cold  water  50  c.c. ; 
ic)  Twice  with  hot  water  30  c.c.  ; 
{d)  Boil  smartly  with  30  c.c.  water. 

After  the  boiling  the  whole  must  be  transferred  to  the  filter 
paper  and  the  filtrate  tested  as  it  drops  from  the  funnel  with 
blue  litmus  paper.  If  an  acid  reaction  is  shown,  another  wash- 
ing with  the  hot  wash  bottle  must  be  given,  but  as  a  rule  the 
filtrate  is  found  to  be  neutral. 

228.  Treatment    of    the    Soluble    Portion.— This 


142        Analysis  and   Valuation  of  Manures       [229,  230 

contains  the  soluble  phosphoric  acid,  together  with  a  certain 
amount  of  H2SO4  and  CaS04. 

The  only  thing  to  be  estimated  is  the  P2O5.  The  liquid  is 
treated  exactly  as  the  solution  of  mineral  phosphate  (paragraphs 
198  and  199),  rejecting  the  lime  precipitate  and  weighing  the 
Mg2P207.  Only  i  gram  of  ammonium  oxalate  and  25  c.c.  of 
MgCl2  mixture  must  be  used. 

229.  Treatment  of  the  Insoluble  Portion.— The 
filter  paper  containing  the  insoluble  part  of  the  manure  is 
transferred  without  drying  to  a  platinum  dish,  and  heated  over 
an  Argand,  very  slightly  at  first,  but  as  soon  as  the  substance  is 
dry  at  the  highest  temperature  obtainable.  When  the  paper  is 
quite  burned,  the  dish  is  allowed  to  cool  and  the  substance 
washed  out  with  dilute  HCl  into  a  beaker  of  the  same  size  as 
that  which  was  used  for  washing  out  the  soluble  portion. 
Twenty  c.c.  of  strong  HCl  are  added,  and  allowed  to  digest  for 
five  minutes  on  the  water  bath.  Fifty  c.c.  of  water  are  added 
to  complete  the  solution  of  any  CaSO^  which  may  be  left. 
This  will  take  about  a  quarter  of  an  hour.  Finally,  the  sand  is 
filtered  off,  washed,  and  treated  as  described  in  the  case  of 
mineral  phosphates  (paragraph  197).  The  filtrate  is  raised  to 
a  boil,  and  ammonia  added  in  excess.  This  precipitates 
all  the  P2O5  left  by  the  water,  in  combination  with  iron, 
aluminium,  and  lime.  It  is  filtered  off,  dried,  ignited,  and 
weighed. 

230.  Calculation.  —  From  the  amount  of  Mg2P207 
the  P2O5  is  calculated,  and  the  correction  of  -33  per  cent, 
made  (see  paragraph  200).  The  percentage  thus  found  is 
multiplied  by  99  and  divided  by  71  to  give  the  percentage 
of  soluble  phosphate,  CaPaOe  (the  anhydrous  form  of 
CaH^PaOg). 

For  purposes  of  valuation,  the  P2O5  is  also  calculated  into 


231,  232]     Analysis  of  Superphosphate  of  Lime 


143 


its  equivalent  of  Ca3(P04)2  (multiply  percentage  of  P2O5  by  155 
and  divide  by  71),  and  the  result  entered  thus  : 


— 

I 

II 

Moisture 

Organic  matter  and  combined  water 
Soluble  phosphate  of  lime 
(Equal  to  Ca3(P04)2    . 
Insoluble  phosphates 
Sulphate  of  lime,  &c. 
Sand 

13-90 

lo-ii 

19-69 

(30-82) 

4-20 

45-85 
6-25 

14*55 

9*54 

16-66 

(26-09) 

5-25 
46-51 

7*49 

100-00 

100-00 

231.  A  second  method,  which  is  rather  more  scientific, 
is  as  follows :  Moisture^  organic  matter^  and  soluble  phosphoric 
acid  are  estimated  as  before. 

Totdil  phosphate  and  lime.  Two  grams  are  weighed  out  and 
treated  exactly  as  though  a  sample  of  bones,  CaC03,  sand,  and 
Mg2P207  were  being  weighed. 

232.  Calculation. — The  soluble  phosphate  is  calculated 
as  before,  together  with  its  equivalent  in  tribasic  phosphate 
of  lime.  The  total  P2O5  is  calculated  into  CaaPgOg.  From 
this  is  subtracted  the  CagPaOg  which  has  been  calculated  as 
equivalent  to  the  soluble  phosphoric  acid.  The  remainder  is 
the  insoluble  phosphate  of  lime. 

From  the  weight  of  CaCOg  the  percentage  of  CaO  is  calcu- 
lated (multiply  by  -56).  From  this  is  subtracted  the  amount 
of  CaO  contained  in  the  soluble  CaPgOg  and  the  insoluble 
CajjPgOg,  and  the  remainder  is  calculated  out  as  CaS04. 

These  calculations  from  the  CaCOs  precipitate  may  be 
simply  and  rapidly  done  as  follows  : 

Subtract  the  soluble  from  the  total  P2O5 ;  result  =  insoluble 
P2O5. 


144  Analysis  and  Valuation  of  Manures  [233 

Subtract  soluble  P2O5  from  CaP205 ;  result  =  lime  in 
soluble  phosphate. 

Subtract  insoluble  P2O5  from  insoluble  Ca2P208;  result 
=  lime  in  insoluble  phosphate. 

Add  CaO  in  CaPaOg  to  CaO  in  CaaPgOg ;  result  =  CaO 
combined  with  P2O5. 

Subtract  this  last  amount  from  total  CaO ;  result  =  CaO 
combined  with  SO3.  Multiply  this  amount  by  17  and  divide 
by  7  ;  result  =  percentage  of  CaSO^.     Enter  results  as 

Moisture .         .         .         .         .         .         •  1 5  'OO 

Organic  matter          .....  i2*oo 

Soluble  phosphate    .....  i8-oo 

Equal  to  Ca3(PO,)„ (28-28) 

Insoluble  phosphate .         ....  6-oo 
Sulphate  of  lime        .         .         .         .         .41-95 

Alkalis,  &c -55 

Sand 6-50 

loo-oo 

233.  Dissolved  Bones  and  Guanoes  with  an  Acid 
Reaction  are  analysed  by  one  of  the  above  methods  with 
the  additional  determination  of  N.  This  is  best  done  by  the 
acid  method,  but  should  the  soda  lime  be  preferred,  a  difficulty 
will  be  met  with  in  the  mixing  of  the  pasty  material  with  soda 
lime.  This  is  overcome  as  follows  :  From  i  to  2  grams  are 
weighed  out  on  a  watch  glass  and  covered  over  with  about 
4  grams  of  gypsum.  The  watch  glass  with  its  contents  is  then 
left  in  a  desiccator.  In  about  half-an-hour  the  substance  is 
removed  to  a  mortar,  rinsing  out  the  watch  glass  with  fine  sand 
which  has  been  well  ignited.  The  mass  will  be  now  fairly  dry, 
and  by  adding  sand  in  small  quantities  at  a  time,  grinding 
with  the  pestle  after  every  addition,  it  will  soon  become  per- 
fectly powdered.  It  may  then  be  mixed  with  soda  lime,  and 
proceeded  with  as  described  in  paragraph  88. 

The  following  are  typical  analyses  of  dissolved  bones  : 


234,  235]     Analysis  of  Supe^'phosphate  of  Lime  145 


I 

II 

Moisture 

♦Organic  matter  . 
Soluble  phosphate 

(Equal  to  Ca3(P04)2 
Insoluble  phosphate 
Calcic  sulphate,  &c. 
Sand   . 

14-43 
22-01 
12-62 

{19-75) 
11-09 

33-64 

6-21 

19-40 

21-67 

8-46 

(13-25) 

20-70 

27-08 

2-69 

loo-oo 

100 -oo 

♦Containing  nitrogen    .... 
Equal  to  ammonia        .... 

1-38 

1-66 

2-59 
3-14 

ANALYSIS  OF  REFUSE  MANURES 

234.  This  name  is  used  simply  for  want  of  a  better  ;  but  it 
does  not  exactly  express  what  is  meant.  Thus,  fish  is,  in  the 
strict  meaning  of  the  term,  a  refuse  material,  but  in  practice  it 
would  be  analysed  as  already  described  under  the  heading  of 
guano.  The  manures  analysed  according  to  the  method  put 
forward  in  this  article  all  contain  small  amounts  of  P2O5,  and 
relatively  very  large  percentages  of  oxide  of  iron  and  alumina, 
together  with  large  quantities  of  organic  matter.  The  more 
common  of  these  ^lxq  farmyard  manure^  nightsoil  {corporation 
manure),  shoddy,  hair,  blood,  horn,  and  soot.  The  most  im- 
portant constituent  is  generally  nitrogen. 

235.  Method  of  Analysis. 


Burn  oflF 

organic  matter.     Treat  with  HCl,  and  filter. 

Precipitate  con- 
sists of  sand 
and  insoluble 
matter. 
Weigh. 

Filtrate.     Add  ammonia  in  excess,  and  filter. 

Precipitate.  Weigh  as  Fe,0,,  AI2O,, 
and  P.O.,.     Re-dissolve  in  HCl 
and  HNO,.     Boil  nearly  to  dry- 
ness.    Add  NH3,  then  HNO3. 
Heat  to  85"  C.  and  add  ammo- 
nium molybdate.    Filter.   Reject 
filtrate.     Dissolve  precipitate  in 
NH3.     Add   magnesia   mixture 
and  weigh  ppt.  as  Mg^.f)^. 

Filtrate.      Boil 
and  add  am- 
monium oxa- 
late.    Filter. 
Burn  ppt.  and 
weigh         as 
CaCOj. 

146         Analysis  and  Valuation  of  Manures      [236-239 

236.  Moisture. — Two  grams  are  dried  at  100°  C.  as 
usual. 

237-  Organic  Matter. — Two  grams  are  weighed  out  in  a 
platinum  dish,  and  ignited  until  of  constant  weight.  The  loss 
gives  moisture  and  organic  matter. 

238.  Sand. — The  ash  left  after  burning  is  dissolved  in 
strong  HCl,  diluted,  and  filtered.  The  sand  on  the  filter  is 
washed,  ignited,  and  weighed. 

239.  Phosphoric  Acid.— The  filtrate  from  the  sand  is 
raised  to  a  boil  and  excess  of  ammonia  added.  The  precipi- 
tate is  allowed  to  settle  and  washed  twice  by  decantation.  It  is 
then  dissolved  in  HCl,  boiled,  re-precipitated  with  ammonia, 
allowed  to  settle  again,  and  washed  well  by  decantation.  When 
fairly  clean  it  is  transferred  to  the  filter,  washed  with  hot  water, 
dried,  ignited,  and  weighed,  the  amount  being  entered  as 
ammonia  precipitate.  The  ignited  mass  is  then  re-dissolved  by 
digestion  on  the  water  bath  with  strong  HCl.  The  solution  is 
boiled  down  nearly  to  dryness.  Ten  c.c.  of  dilute  HNO3  (3-1) 
are  added  with  50  c.c.  of  water,  then  ammonia  until  nearly  neutral. 
Excess  of  HNO3  is  next  added,  and  the  solution  heated  to 
85°  C.  This  heating  and  the  next  operation  are  most  con- 
veniently carried  out  in  an  8-oz.  conical  flask  fitted  with  an 
india-rubber  stopper.  Forty  c.c.  of  ammonium  molybdate  solu- 
tion are  added  to  the  liquid  and  the  whole  shaken  up  well  for 
three  minutes,  then  placed  on  the  water  bath  for  twenty  minutes 
to  settle.  The  yellow  precipitate  is  filtered  off  and  washed  with 
dilute  HNO3.  To  the  filtrate  another  10  c.c.  of  molybdate 
solution  are  added,  and  if  further  precipitation  occurs  it  is  heated 
to  85°  C,  shaken  up  again,  and  the  operation  repeated.  The 
washed  precipitate  is  dissolved  in  dilute  ammonia,  which  must  be 
poured  into  the  filter  so  that  only  the  soluble  portion  may  come 
through.  To  the  ammoniacal  solution  10  c.c.  of  magnesia 
mixture  are  added,  drop  by  drop,  stirring  all  the  while ;  10  c.c.  of 


240-242] 


Analysis  of  Refuse  Manures 


147 


strong  NH3  solution  are  then  added,  and  the  liquid  is  allowed 
to  stand  two  hours.  The  magnesium  ammonium  phosphate  is 
filtered  off,  washed  with  ammonia,  dried,  ignited,  and  weighed 
as  usual. 

The  correction  necessary  in  this  case  is  very  small,  and  must 
be  obtained  by  measuring  the  filtrate  and  washings.  For  every 
60  c.c.  I  milligram  is  added  to  the  weight  of  the  ignited 
precipitate. 

240.  Lime. — The  lime  is  contained  in  the  filtrate  from  the 
ammonia  precipitate  and  the  washings  after  re-precipitation.  It 
is  precipitated  by  ammonium  oxalate  and  weighed  as  usual, 
Should  the  precipitate  be  very  small — i.e. ,  less  than  -05  gram — 
it  is  ignited  for  twenty  minutes  in  the  Fletcher  muffle  and 
weighed  as  CaO. 

241.  Nitrogen. — Best  determined  by  the  acid  method 
(paragraphs  90-95). 

242.  Calculation.— From  the  MggPsOy  are  calculated 
first  the  P2O5,  then  the  CagPgOs  to  which  this  is  equivalent. 
From  the  CaCOa  the  CaO  is  calculated,  and  from  this  the  CaO 
as  CagPaOg  is  subtracted.  The  remainder  is  calculated  back 
into  CaCO.,,  and  the  analysis  entered  as  follows  : 


Soot 

Shoddy 

Rabbits' 
dung 

Dried 
sewage 

Sugar 
scum 

Moisture . 
"Organic  matter 
Phosphate  of  lime     . 
Carbonate  of  Hme     . 
Oxide  of  iron  and  \ 
alumina,  &c.           j 
Sand 

10-42 
45-28 

20 -06 

8-99 

15-25 

977 
68-85 

5 -20 

5-04 

II.I4 

67-30 

28-71 

1-49 

I -16 

.•34 

14-55 
41-80 
16-37 

9-58 
17-70 

46-65 

1777 
9-69 
6*09 

14-98 
4-82 

100 -oo 

100 -OO 

100 '00 

100 -oo 

loo-oo 

♦Containing  nitrogen 
Equal  to  ammonia 

3-59 
4-36 

5-65 
6-86 

•87 

1-05 

2-64 
3-21 

•44 

•53 

L2 


148         Analysis  and  Valuation  of  Manures      [243-246 

ANALYSIS  OF  MANURE  CAKES 

243.  Such  substances  as  rape  cake,  castor-bean  cake,  and 
damaged  cotton  and  linseed  cakes  are  often  used  as  manures. 
The  principal  manurial  constituent  is,  of  course,  nitrogen,  but 
ir)  addition  to  this  there  is  always  a  certain  quantity  of  phos- 
phoric acid  in  the  ash  usually  combined  with  an  alkali  metal. 

244.  Method  of  Analysis. 


Burn.     Treat  ash  with  HCl.     Filter. 


Precipitate.     Weigh  as 


Filtrate.  Add  ammonia  and  calcium 
chloride.  Filter,  and  weigh  pre- 
cipitate as  CagP^Og. 


245.  Moisture,  nitrogen,  and  organic  matter  are  estimated 
as  in  guano. 

246.  Sand  and  Calcic  Phosphate.— Two  grams  of  the 
substance  are  weighed  out  in  a  platinum  dish  and  burned,  with 
the  precautions  described  in  the  analysis  of  feeding  cakes. 
The  ash  is  transferred  to  a  small  beaker,  and  dissolved  in  about 
20  c.c.  of  strong  hydrochloric  acid.  The  insoluble  portion  is 
filtered  off,  washed  with  hot  water,  burned  as  described  under 
the  estimation  of  sand  in  mineral  phosphates,  and  weighed. 

The  filtrate  from  the  sand  contains  the  phosphoric  acid, 
together  with  lime  and  alkalis.  Of  course  this  phosphoric 
acid  may  be  determined  either  by  the  citric  acid  or  the 
molybdate  method,  but  it  is  customary  to  determine  it  by  the 
simple  method  indicated  in  the  last  table.  The  liquid  must  be 
raised  to  the  boiling-point,  about  10  c.c.  of  the  ordinary  labora- 
tory solution  of  calcium  chloride  added,  then  excess  of  ammonia. 
The  precipitate  of  calcium  phosphate  so  formed  must  be 
filtered  rapidly,  washed,  and  weighed  as  CaaPgOg. 

From  this  weight  the  amount  of  phosphoric  acid  may  be 
calculated,  or  the  result  may  be  set  out  in  this  form  : 


247-250]  Analysis  of  Manure  Cakes 


149 


1 

Rape  cake 

Castor  cake 

Cotton  cake 

Moisture  .         .         .      '  . 
•Organic  matter 
Calcic  phosphate 
Alkalis,  &c.       . 
Sand         .... 

9-54 
8o-o2 

5-95 

•84 

3-65 

1072 
82-88 

5-29 
•42 
•69 

IO-8I 

82-49 

5-55 

•50 

-65 

lOO'OO 

100 -oo 

icx)-oo 

♦Containing  N  .         .         .     478 
NH,        .         .         .         .     5-8i 

4-94 
5-99 

7-56 
9-18 

ANALYSIS  OF  POTASSIC  MANURES:  KAINIT, 
MURIATE  OF  POTASH,  SULPHATE  OF  POT- 
ASH, &c. 

247.  As  a  rule,  nothing  but  \S\q  potash  is  estimated  in  these 
substances.  Occasionally,  however,  a  somewhat  fuller  analysis 
is  required. 

248.  Moisture  is  estimated  as  usual. 

249.  Sanctis  estimated  by  dissolving  in  water  slightly  acidu- 
lated with  HCl,  filtering,  washing,  and  igniting  and  weighing. 

The  other  two  substances  ^xq  potash  and  magnesia. 

250.  Potash. — The  simplest  method  is  as  follows :  Weigh 
out  '5  gram,  dissolve  in  water  with  a  small  amount  of  dilute 
HCl,  filter  off  the  sand  and  wash  well.  To  the  filtrate  add 
about  "5  gram  pure  NaCl  and  15  c.c.  PtCl4  solution  (10  grams 
PtCl4  in  100  c.c.  H2O).  Evaporate  exactly  as  described  in  para- 
graph 33  to  a  pasty  state.  Add  2  c.c.  PtCl4  solution.  Shake 
round  the  beaker,  allow  to  stand  for  five  minutes,  and  filter 
through  two  counterpoised  papers.  Allow  the  whole  of  the 
liquid  to  run  through,  then  with  the  least  possible  quantity  of 
PtCl4  solution  (not  more  than  3  c.c.)  rinse  the  beaker  and  wash 
the  precipitate.  When  the  liquid  has  again  entirely  passed 
through,  the  rest  of  the  precipitate  must   be  removed  to  the 


150         Analysis  and  Valuation  of  Manures      [251,  252 

paper  with  strong  alcohol,  well  washed,  dried,  and  weighed  as 
described  in  paragraph  32.  The  NaCl  is  added  to  turn  all 
K2SO4  into  KCl.  The  preliminary  washing  with  PtClj  is  to 
remove  any  double  compounds  of  platinum  with  magnesium 
and  sodium,  which  would  be  insoluble  in  alcohol. 

251.  Another  Method. — Weigh  out  about  -5  gram  of  the 
substance.  Dissolve  in  water.  To  the  solution,  which  con- 
tains the  sand  in  suspension,  add  Ba(0H)2  solution  until 
alkaline.  Allow  the  precipitate  to  settle,  keeping  the  beaker 
on  the  water  bath.  Filter  rapidly,  and  wash  well  with  boiling 
water.  The  precipitate  consists  of  barium  sulphate  and  mag- 
nesia, which  may  be  rejected.  Make  the  solution  acid  with 
HCl.  Raise  it  to  boiling-point,  then  add  hot  BaClg  drop  by 
drop,  until  ho  further  precipitate  occurs.  This  is  best  done  by 
keeping  the  beaker  on  a  water  bath,  and  allowing  the  precipitate 
to  subside  after  each  few  drops.  When  no  further  precipitate 
forms  there  will  be  a  small  amount  of  BaCl2  in  solution, 
together  with  all  the  potassium  in  the  state  of  chloride.  The 
barium  must  be  removed  by  a  drop  or  two  of  dilute  H2SO4 
and  the  BaS04  filtered  off  and  washed.  The  filtrate  is  evapo- 
rated down  and  estimated  as  in  paragraphs  33-35.  As  small 
quantities  of  Mg  and  Na  may  be  present,  it  is  best  to  moisten 
the  pasty  substance  with  a  little  PtCl4  solution  and  decant 
through  the  filter  paper  before  using  alcohol. 

ANALYSIS   OF   AMMONIUM   SALTS 

252.  As  these  salts  are  generally  prepared  as  by  pro- 
ducts in  coal  gas  manufacture,  it  is  always  possible  that  they 
may  contain  traces  of  ammonium  sulphocyanate,  which  is  a 
strong  plant  poison.  They  should  therefore  be  tested  quali- 
tatively for  NHjCNS  with  FeaClo,  which  should  give  no  red 
colouration. 


253-258]  Analysis  of  Ammonium  Salts  151 

253.  Estimation  of  Ammonia. — This  may  be  done  by 
the  soda  lime  method.  As  the  substance  is  often  damp,  and 
would  give  off  ammonia  as  soon  as  it  touched  the  alkaline 
substance,  it  should  be  well  mixed  with  gypsum  before  adding 
to  the  soda  lime.  About  -5  gram  should  be  used,  and  the  tube 
should  be  about  12  inches  long. 

It  is  very  seldom  that  anything  else  is  estimated  in  ammo- 
nium salts,  but  it  is  sometimes  necessary  to  estimate  the 
moisture  and  '  ash  ' — i.e.^  the  non- volatile  matter. 

254.  Moisture  is  estimated  as  usual. 

255.  Non-volatile  matter  is  estimated  by  weighing  out 
2  grams  in  a  platinum  capsule  and  heating  on  an  Argand  until 
it  ceases  to  fume,  then  weighing  the  residue.  The  burner 
should  be  very  low  to  begin  with,  but  the  temperature  may  be 
increased  as  the  operation  proceeds,  using  a  red  heat  to  drive 
off  the  last  traces  of  volatile  matter, 

ANALYSIS   OF   NITRATE   OF   SODA 

256.  This  substance  is  generally  guaranteed  to  contain 
95  per  cent,  pure  NaNOs,  the  impurities  being  sand,  together 
with  sulphate  and  chloride  of  sodium.  The  chlorine  and 
sulphuric  acid  should  be  determined  as  in  paragraphs  28-31, 
and  69-70. 

257.  Nitric  Acid. — Any  of  the  methods  described  in  the 
chapter  on  nitrogen  determination  may  be  used,  Ulsch's  being 
the  most  easily  managed. 

ANALYSIS   OF  COMPOUND   MANURES 

258.  This  is  a  somewhat  comprehensive  term,  including 
all  kinds  of  special  manure.  Ordinarily  a  compound  manure 
will  be  found  to  consist  of  mineral  or  bone  superphosphate 
mixed  with  some  nitrogenous  substance.     It  will  often  contain 


152  Analysis  and  Valuation  of  Manures  [259 

salts  of  potassium,  and  sometimes  nitrates.  The  first  thing  to 
do  is,  of  course,  to  find  out  what  the  manure  consists  of.  The 
following  tests  may  be  used  : 

Experiment  I, — Make  into  a  paste  with  water  and  add  a 
piece  of  blue  litmus  paper.  If  it  be  strongly  acid,  the  soluble 
P2O5  must  be  estimated. 

Experiment  II. — Boil  a  small  quantity  (about  4  grams) 
with  100  c.c.  distilled  water  ;  filter,  and  divide  the  filtrate  into 
two  parts,  A  and  B. 

{A)  Add  I  C.C.  indigo  solution  and  50  c.c.  strong  H2SO4. 
Should  the  indigo  bleach,  the  manure  contains  nitrates. 

{B)  Add  5  c.c.  strong  H2SO4.  Boil  to  dryness  in  a 
platinum  dish ;  ignite  the  residue  until  it  no  longer  fumes. 
Dissolve  in  alcohol;  filter.  To  the  filtrate  add  i  c.c.  of 
PtCl4  solution.     A  yellow  precipitate  indicates  potash. 

If  the  substance  contain  soluble  phosphoric  acid,  it  must 
be  analysed  exactly  like  a  superphosphate. 

If  the  substance  be  not  acid,  it  must  be  analysed  exactly 
like  a  sample  of  bones. 

If  the  substance  contain  N2O5  the  nitrogen  must  be  esti- 
mated by  the  modified  acid  method. 

If  the  substance  contain  potash,  2  grams  of  the  substance 
are  ignited  at  a  dull  red  heat  until  all  the  organic  matter  and 
salts  of  ammonia  have  been  driven  off.  The  residue  is  boiled 
with  water,  filtered,  and  washed.  The  K2O  in  the  washings  is 
estimated  by  one  of  the  two  methods  given  under  potash 
manures y  paragraphs  250  and  251. 

VALUATION   OF   MANURES   BY  ANALYSIS 

259.  The  word  value  has  two  very  distinct  meanings.  It 
may  either  indicate  the  price  which  must  be  paid  when  purchas- 
ing a  manure,  or  it  may  mean  the  profit  which  is  to  be  obtained 


260,  261]       Valuation  of  Manures  by  Analysis  153 

by  using  it.  Thus,  ii  is  by  no  means  proved — in  fact,  it  is 
highly  improbable — that  the  soluble  phosphate  in  dissolved 
bones  is  any  more  efficient  as  a  manure  than  that  contained  in 
a  mineral  superphosphate.  Therefore,  so  far  as  the  produce  of 
this  manurial  constituent  is  concerned,  it  is  of  the  same  value 
in  each  case ;  whereas  commercially  the  price  of  the  soluble 
phosphate  in  bones  is  very  much  higher  than  that  in  mineral 
superphosphate. 

260.  Definition  of  a  Unit. — The  commercial  unit  of  any 
manurial  constituent  is  the  hundredth  part  of  a  ton.  Thus,  if 
a  mineral  superphosphate  be  found  to  contain  27*85  per  cent 
of  soluble  phosphate,  it  is  said  to  contain  27*85  units  of  soluble 
phosphate  per  ton. 

N.B. — The  commercial  unit  of  soluble  phosphate  is  really 
the  unit  of  CagPaOg  equivalent  to  the  soluble  phosphate ;  thus 
it  is  sometimes  quoted  as  '  phosphate  made  soluble.' 

261.  Valuation  by  Units. — Of  course  the  prices  of 
various  manures  fluctuate  considerably,  and  it  is  therefore 
necessary,  when  an  exact  valuation  is  required,  to  know  the 
present  prices  per  unit.  These  are  published  every  month  by 
some  of  the  principal  manure  merchants,  and  also  by  several 
of  the  leading  agricultural  societies.  The  following  table  shows 
the  form  in  which  these  prices  are  published,  and  gives  an  idea 
of  what  those  prices  are  per  unit : 

Phosphate  made  soluble  (CaaPgOg)  :  s.    d.  s.    d. 

From  raw  bones 

From  bone  ash 

From  mineral  ......     2 

Insoluble  phosphate  (CaaPgO.,)  : 

In  natural  guano 

In  bones  or  fish  manures   . 


In  ground  minerals   . 

In  basic  slag     . 

In  mineral  superphosphate 


2 

8 

to 

2 

10 

2 

8 

)» 

2 

II 

2 

2 

>> 

2 

5 

2 

0 

>> 

2 

4 

I 

3 

j> 

I 

8 

I 

0 

j> 

I 

3 

0 

10^ 

j> 

I 

I 

0 

6 

»> 

0 

8 

154 


Analysis  and  Valuation  of  Manures  [262 


Phosphoric  acid  (PPs) : 

s. 

d. 

s. 

d. 

Varies  according  to  source 

4 

9 

to 

6 

2 

Ammonia  (NH)  : 

Peruvian  guano  (6-9  per  cent.  NH.,) 

18 

6 

>» 

22 

6 

Peruvian  guano  (3-5  per  cent.  NHj) 

15 

0 

5J 

18 

0 

Ammoniated  Peruvian  guano  (lo-ii  per 

cent.  NH3) 

13 

6 

SJ 

14 

6 

Ichaboe  guano  (lo-ii  per  cent.  NH.,) 

17 

0 

>> 

18 

0 

Rape  meal 

13 

6 

>> 

17 

0 

Ground  bones 

10 

0 

>5 

II 

0 

Sulphate  of  ammonia       .... 

8 

9 

>J 

9 

6 

Fish  manures 

10 

0 

■>■> 

II 

0 

Shoddy,  high    quality   (over  8  per  cent. 

NH3) 

5 

0 

,, 

7 

0 

Shoddy,    low    quality    (ground    leather, 

hoof,  and  horn) 

3 

0 

,, 

5 

0 

Equivalent  to  nitrogen  in  NaNOs     . 

10 

0 

J> 

II 

0 

Which  is  equal  to  NaNOg 

2 

I 

55 

2 

3 

Potash  (K^O) : 

In  kainit 

2 

9 

55 

3 

5 

In  sulphate  of  potash        .... 

3 

8 

,, 

4 

I 

Equivalent  in  muriate  of  potash 

3 

4 

>5 

3 

8 

262.  To  calculate  the  price  per  ton  of  a  manure.  Mul- 
tiply the  percentage  of  each  manurial  constituent  by  its  price 
per  unit,  and  add  up  the  amounts  so  obtained. 

Take,  for  instance,  a  compound  manure  of  the  following 
composition  : 


Moisture     . 

.     13-30 

♦Organic  matter   . 

.     15-24 

Soluble  phosphate 

.       7-42 

(Equal  to  Ca3P,Oj     . 

.         .    (II-6I) 

Insoluble  phosphate    . 

.     22-30 

•fCalcic  sulphate,  &c.     . 

.     39-04 

Sand. 

.       270 
loo-oo 

♦Containing  N 

% 

•88 

Equal  to  NH3     . 

.       I -07 

f  Containing  KgO  . 

.         5-22 

And  N,0,  .         .         .         . 

.     470 

Equal  to  NaNOg 

.      7-37 

263] 


Valuation  of  Manures  by  Analysis 


155 


The  price  may  be  added  up  in  this  manner : 

s.  d. 
CaaPyOy  made  soluble  (bone)  11 -Six    2  9     = 


Insoluble  Ca^P.^g  (bone) 
NH3  (bone)      '    . 
K2O  (say  kainit)  . 
NaNO, 


22-30  X  I  5 
1-07  X  10  O 
5*22  X  30 
7-37  X     2   2 


I    II 
I    II 


5    8| 


The  market  price  of  such  a  manure  would  therefore  be 
£i^  5^.  ^\d.  plus  the  cost  of  mixing  the  ingredients. 

263.  Valuation  of  Mineral  Phosphates.— In  this 
country,  now  that  the  coprolite  beds  are  almost  used  up,  the 
use  of  mineral  phosphates  in  the  raw  state  as  manures  is  quite 
exceptional.  Therefore  the  valuation  is  based  on  the  readiness 
with  which  they  are  converted  into  superphosphate  and  on 
the  quality  of  that  product  when  made.  The  principal 
impurities  which  influence  superphosphate  manufacture  are 
the  oxides  of  iron  and  aluminium,  carbonate  of  lime,  and 
fluorides.  The  extent  to  which  these  impurities  are  detri- 
mental is  partly  shown  in  the  following  table,  which  gives  the 
amount  of  pure  H2SO4,  oil  of  vitriol  S.G.  i"6,  and  oil  of 
vitriol  S.G.  i'55  absorbed  by  100  parts  of  each  substance  : 


Substances 

Pure  H3SO, 

Oil  of  vitriol 
S.G.  1-6 

Oil  of  vitriol 
S.G.  1-55 

Substances  formed 

Ca3P,0« 

CaC03 

CaF, 

Fe,03 

Al,03 

63-2 

97-5 
79-6 
61 -2 
95-1 

94 
146 
118 

91 
141 

100 
126 

97 
151 

CaH^PgOs  and  CaSO^ 
CO.,  and  CaSO^ 
HFandCaSO, 
Fe,(SO,)3 
A1,(S0,)3 

Against  this  waste  of  sulphuric  acid  must  be  placed  the  fact 
that  a  certain  amount  of  CaCOa  is  somewhat  beneficial.  The 
carbonic  acid  gas  escaping  within  the  mass  promotes  spongi- 
ness  and  lightness  in  the  manure,  and  facilitates  drying. 

In  the  case  of  CaFg,  the  whole  of  the  HF  does  not  escape, 


156  Analysis  and  Valuation  of  Manures  [263 

but  attacks  any  silica  which  may  be  present,  forming  SiF4,  and 
this  in  its  turn  may  be  acted  upon  by  water,  forming  Si02  and 
H^SiFe. 

Thus  it  will  be  seen  that  the  exact  valuation  of  a  mineral 
phosphate  by  analysis  would  entail  a  very  complex  calculation. 
A  rough  method  is  very  often  employed  based  upon  the  per- 
centages of  CagPgOg,  Fe203,  and  AI2O3,  the  other  impurities 
being  neglected.  When  less  than  3  per  cent,  of  the  mixed 
oxides  of  iron  and  aluminium  is  present,  the  valuation  is  calcu- 
lated entirely  from  the  percentage  of  CaaPgOg.  When  more 
than  3  per  cent,  is  present,  the  excess  is  multipHed  by  2 
and  subtracted  from  the  percentage  of  phosphate.  Thus,  sup- 
posing that  analysis  showed  a  mineral  to  contain  80  per  cent, 
of  CagPsOg  and  5  per  cent,  of  oxides  of  iron  and  aluminium, 
the  excess  of  2  per  cent,  over  the  3  allowed  would  be 
doubled  and  subtracted  from  the  80.  The  mineral  would 
be  then  valued  as  containing  76  per  cent.  Ca3P208.  In  fact, 
many  vendors  would  sell  it  as  guaranteed  to  contain  76  per 
cjiit.  phosphate  of  lime. 


PART   VII 

SOIL  ANALYSIS 

Soil  analysis  leads  to  no  such  accurate  valuation  of  a  soil 
as  manure  analysis  does  of  a  manure.  Hence  it  is  not  a  true 
commercial  analysis.  An  analyst  is  frequently  asked  to  in- 
vestigate a  soil  with  a  view  to  advising  the  farmer  as  to  its 
treatment.  This  is  an  exceedingly  difficult  problem,  involving 
as  it  does  many  conditions  which  cannot  be  determined  in  the 
laboratory.  Even  in  the  laboratory  the  problem  to  be  faced 
by  the  chemist  presents  many  difficulties.  Perhaps  this  will  be 
best  understood  by  reading  the  following  excerpt  from  a  paper 
read  before  the  Chemical  Society  by  Dr.  Bernard  Dyer  in 
1894: 

'  The  chemical  analysis  of  soils,  which  in  the  early  days  of 
agricultural  chemistry  was  looked  upon  as  Hkely  to  be  of 
great  practical  use  in  agriculture,  was  soon  found  to  be,  as 
ordinarily  practised,  of  very  Hmited  value.  Determinations  in 
the  soil  of  the  total  quantities  of  the  more  important  mineral 
elements  of  plant  food  have  been  long  recognised  as  affording 
useful  information  only  in  exceptional  cases  ;  and  even  in  these 
exceptional  cases  the  results  obtained  have  rather  afforded 
"  probable  indications "  than  absolute  information.  The 
reason,  as  has  often  been  pointed  out,  is  that  an  analysis  of 
soil,  as  ordinarily  made,  shows  the  total  percentage  of  its  con- 
stituents, or  at  any  rate,  the  percentage  dissolved  by  strong 


15B  Soil  Analysis  [264 

mineral  acids,  without  reference  to  the  fact  that  only  a  very 
small  proportion  of  this  total  may  be  available  for  plant  use' 

We  know  that  plants  can  only  take  up  food  from  the  soil  in 
a  state  of  solution,  the  chief  solvents  being  water  saturated 
with  CO2  or  the  acid  excretions  of  the  plants'  own  roots. 

Dr.  Dyer  has  estimated  the  acid  contents  of  the  root  sap  of 
over  a  hundred  varieties  of  plants,  and  finds  that,  on  the  average, 
a  I  per  cent,  solution  of  citric  acid  is  very  similar  in  its  action 
to  this  acid  secretion. 

A  long  series  of  experiments  on  Rothamsted  soils,  of  which 
the  history  was  known,  confirmed  his  opinion  that  a  citric  acid 
solution  of  this  strength  would  give  an  accurate  idea  of  the 
available  potash  and  phosphoric  acid  in  the  soils. 

As  this  method  occupies  some  time,  it  is  described  first.' 
The  student  should  start  this  analysis,  and  whilst  it  is  standing 
he  should  proceed  with  the  fuller  analyses  described  in  para- 
graph 270. 

264.  Solubility  in  Citric  Acid  Solution. — Take  a  Win- 
chester quart  bottle  which  has  been  used  for  the  storage  of  strong 
acids,  and  which,  therefore,  will  be  unlikely  to  yield  up  potash, 
&c.,  to  the  citric  acid  solution,  and  rinse  it  thoroughly.  Weigh 
out  200  grams  of  air-dried  soil  and  place  it  in  the  Winchester. 
Dissolve  20  grams  of  citric  acid  in  2  litres  of  distilled  water 
and  pour  it  over  the  soil.  Stopper  the  bottle  and  shake  up 
thoroughly.  This  shaking  must  be  repeated  several  times  each 
day  for  seven  days.  At  the  end  of  seven  days  the  solution  is 
decanted  through  a  large  filter,  two  portions,  each  of  500  c.c, 
are  collected,  and  treated  as  described  in  the  next  two  para- 
graphs. 

At  the  same  time  weigh  out  50  grams  of  the  same  air-dried 
soil  in  a  tared  evaporating  basin.  Place  this  in  a  steam  oven 
and  leave  for  about  five  hours ;  after  this  weigh  every  twenty 
minutes  until   the  weight  is   constant.      The   loss   represents 


265-267]  Soil  Analysis  i^g 

moisture.     From  this  estimation  calculate  the  quantity  of  dry 
soil  in  the  200  grams. 

265.  Available  Phosphoric  Acid.— Evaporate  500  c.c.  of 
the  clear  liquid  on  a  water  bath  until  it  measures  about  100  c.c. 
Allow  it  to  cool  thoroughly  and  add  40  c.c.  clear  ammonium 
molybdate  dissolved  in  nitric  acid  (paragraph  208).  Allow  to 
stand  for  forty-eight  hours  with  occasional  stirring.  Decant  the 
liquid  through  a  filter  and  wash  several  times,  first  with  dilute 
nitric  acid  (1-4),  then  with  pure  water  in  very  small  doses,  and 
finally  transfer  to  the  filter  and  wash  free  from  excess  of  acid. 
The  ammonium  phospho-molybdate  is  dissolved  in  dilute  am- 
monia, allowing  the  solution  to  run  into  a  weighed  platinum 
dish.  When  the  filter  has  been  washed  two  or  three  times,  the 
dish  is  placed  on  the  water  bath  and  the  ammoniacal  liquor 
evaporated  to  dryness.  It  is  finally  dried  in  a  steam  oven  and 
weighed.  The  residue  contains  3  "5  per  cent,  of  its  weight  of 
phosphoric  acid  (P2O5). 

266.  Available  Potash. — Five  hundred  c.c.  of  the  clear 
liquid  is  evaporated  on  the  water  bath  with  a  little  strong  hydro- 
chloric acid  ;  when  quite  dry  it  is  gently  heated  over  an  Argand 
until  all  the  organic  matter  is  burned  oif  and  the  residue  is  nearly 
white.  This  residue  is  dissolved  in  HCl,  and  evaporated  slowly 
with  5  c.c.  platinum  chloride  solution  (10  per  cent.).  If  the 
evaporation  be  conducted  slowly,  the  platinum  potassium 
chloride  settles  out  well,  in  spite  of  the  various  salts  present. 
When  nearly  dry,  decant  through  a  filter  paper,  wash  twice  with 
small  quantities  of  platinum  chloride  solution,  and  finally  with 
strong  alcohol.  When  the  alcohol  comes  through  clear,  dry  the 
filter  at  100°,  then  wash  through  with  hot  water  into  a  tared  dish. 
Evaporate  to  dryness,  dry  in  a  water  oven  and  weigh.  Cal- 
culate the  percentage  of  potash  as  described  in  paragraph  36. 

267.  Calculation. — The  200  grams  originally  dissolved  in 
the  citric  acid  contained  a  certain  amount  of  moisture,  Which 


i6o  Soil  Analysts  [268-270 

has  been  estimated.  Hence  we  know  how  much  dry  soil  the 
200  grams  contained.  One  quarter  of  this — i.e.^  something 
less  than  50  grams — is  used  for  each  estimation. 

268.  Conclusion. — Dr.  Dyer's  conclusion  from  many 
analyses  was  that 

{a)  '  When  a  soil  is  found  to  contain  so  little  as  about  coi 
per  cent,  of  phosphoric  acid  (P2O5)  soluble  in  a  i  per  cent, 
solution  of  citric  acid,  it  would  be  justifiable  to  assume  that  it 
stands  in  immediate  need  of  phosphatic  manure.' 

{b)  It  is  difficult — '  more  difficult  than  in  the  case  of 
phosphoric  acid — to  give  any  plausible  suggestion  as  to  what 
percentage  of  citric-acid-soluble  potash  may  be  regarded  as 
marking  the  non-necessity  of  special  potash  applications. 
Probably  this  limit  lies  below  0*005  P^^  cent' 

269.  Full  Analysis  of  Soil. — In  many  cases  a  much  fuller 
analysis  is  required  than  the  one  just  described.  It  is  not  only 
necessary  to  discover  what  plant  food  is  immediately  available, 
but  also  what  stores  of  food  are  locked  up  in  such  a  manner 
that  good  tillage  and  weathering  may  at  some  future  time  bend 
them  to  the  use  of  the  crop.  This  is  generally  done  by  two 
separate  sets  of  operations.  The  first  is  to  analyse  that  portion 
soluble  in  hydrochloric  acid,  and  the  second  to  analyse  the 
insoluble  residue. 


FULL   ANALYSIS   OF  PORTION   SOLUBLE 
IN   HCl 

270.  Preliminary  Operations.— Dry,  finely  powdered 
soil,  prepared  as  directed  in  paragraph  132,  is  such  a  very 
hygroscopic  substance  that  it  is  rather  difficult  to  weigh  out 
accurately.  The  following  method  is  therefore  recommended 
as  avoiding  the  difficulty  : 

Place  about  30  grams  of  the  powdered  soil  in  a  porcelain 


270]  Analysis  of  Portion  Soluble  in  HCl  i6i 

basin,  and  allow  it  to  stand  for  half-an-hour  in  the  balance 
case.     Then  weigh  out  portions  as  follows  : 

{a)  5  grams  in  a  platinum  dish  ; 

{b)  5  grams  in  a  pair  of  watch  glasses  with  clip  ; 

{c)  5  grams  in  a  wide- mouthed  4-oz.  beaker. 

Treat  the  different  portions  as  follows. 

N.B. — Each  of  the  following  operations  occupies  a  consider- 
able length  of  time ;  it  is,  therefore,  best  to  get  them  all  started 
as  nearly  together  as  possible,  so  that  no  time  may  be  wasted. 

{a)  Determination  of  moisture  plus  organic  matter  and  salts 
of  ammonia.  Place  the  dish  containing  the  weighed  portion 
of  soil  on  an  Argand  which  has  its  flame  turned  down  very  low. 
Turn  up  the  flame  very  gradually,  about  once  every  five  minutes, 
until  in  an  hour  it  is  about  as  hot  as  when  used  for  turning 
calcium  oxalate  to  calcium  carbonate.  The  soil  will  turn  darker 
in  colour,  and  then  slowly  lighter,  as  the  carbonised  organic 
matter  is  burned  off".  In  order  that  all  the  hot  soil  may  be 
exposed  to  the  air  it  is  necessary  to  stir  it  occasionally.  To 
do  this  use  a  piece  of  No.  10  B.W.G.  copper  wire  about 
4  inches  long,  having  one  end  flattened  out  for  about  |  inch. 
See  that  the  wire  is  polished,  and  free  from  any  roughness 
which  may  cause  the  soil  to  adhere.  With  this  instrument 
a  little  care  will  enable  the  operator  to  stir  the  powder  without 
causing  any  loss  whatever.  At  least  five  hours  will  be  required 
for  the  complete  oxidation  of  the  organic  matter.  When  that 
time  has  elapsed,  cool  the  dish  in  a  desiccator  and  weigh,  then 
return  to  the  Argand  for  half  an-hour.  Repeat  the  process 
until  no  further  loss  is  sustained.  After  the  burning  has  been 
completed,  this  portion  is  treated  with  HCl  and  used  for  the 
general  analysis  (see  paragraph  271). 

The  reason  for  keeping  the  temperature  below  a  red  heat  is 
to  prevent  the  decomposition  of  the  CaCOa. 


1 62  Soil  Analysis  [270 

{b)  Determination  of  moisture.  This  determination  is  of 
no  value  to  the  farmer,  since  the  moisture  in  any  soil  ex- 
posed to  the  weather  is,  perforce,  a  very  variable  quantity.  It 
is  therefore  only  made  to  enable  the  operator  to  calculate 
out  his  results  as  parts  per  hundred  of  the  perfectly  dry 
sample. 

Remove  the  clip,  and  place  the  watch  glasses  containing 
the  soil  in  the  steam  oven.  In  two  hours  replace  the  clip, 
allow  to  cool  in  a  desiccator,  and  weigh.  Repeat  the  dry- 
ing operation  for  half-an-hour  at  a  time  until  the  weight  is 
constant. 

{c)  Determination  of  sulphuric  and  phosphoric  acids.  Add 
to  the  soil  in  the  beaker  5  c.c.  dilute  HCl,  cover  with  a  clock 
glass,  and  allow  it  to  stand  on  the  top  of  the  steam  oven  until 
effervescence  ceases.  Remove  the  clock  glass,  washing  any 
liquid  condensed  on  it  back  into  the  beaker,  and  add  25  c.c. 
strong  HCl.  Evaporate  to  dryness  on  the  water  bath.  Heat 
for  a  minute  or  two  on  the  sand  bath  until  completely  dry, 
cool,  moisten  with  strong  HCl,  add  25  c.c.  dilute  HCl  (1-2), 
mix  thoroughly  with  a  short  glass  rod,  heat  on  the  water  bath 
until  the  sediment  settles,  and  decant  through  a  filter  into  a 
12-OZ  beaker.  Wash  by  decantation  until  the  washings  are  no 
longer  acid,  reject  the  precipitate,  and  treat  the  liquid  as 
directed  in  the  following  table  : 


Raise  nearly  to  boiling,  add  ammonia  in  slight  excess,  boil,  allow  to 
settle,  filter,  washing  by  decantation. 


Precipitate.  Make  a  hole  through  the 
paper  ;  wash  the  ppt.  into  a  i6-oz. 
beaker  with  dilute  HNO3, removing  the 
last  traces  by  dropping  strong  HNO3 
into  the  filter,  then  washing  with  hot 
water.  Heat  to  85°  C.  Add  25  c.c. 
ammonium  molybdate  solution,  allow 
to  stand  one  hour  in  a  warm  place,  and  determine  PgOj  as  described  in 
paragraph  209. 


Filtrate.  Add  HCl  until 
acid,  boil,  add  hot  BaCL. 
Allow  to  stand  on  water 
bath  for  an  hour,  filter, 
and  weigh  BaSO.,  as  in 
paragraphs  29  and  30. 


271,  272]  General  Analysis  of  the  Burned  Portion      163 

General  Analysis  of  the  Burned  Portion 

271.  Remove  the  substance  left  in  the  platinum  dish, 
after  burning,  to  a  4-oz.  wide-mouthed  beaker,  and  treat  with 
HCl  exactly  in  the  same  manner  as  the  portion  used  for  the 
determination  of  sulphuric  and  phosphoric  acids.  Evaporate 
to  dryness,  and  moisten  with  strong  HCl.  Add  25  c.c.  dilute 
HCl,  filter  and  wash  by  decantation.     Dry,  burn,  and  weigh. 

This  weighing  operation  may  cause  some  little  trouble,  as 
the  dry  silicates  are  very  hygroscopic.  The  weighing  should 
be  performed  as  rapidly  as  possible.  Directly  after  weighing, 
the  dish  with  its  contents  should  be  returned  to  the  Argand, 
and  allowed  to  cool  again  in  the  desiccator.  Before  weighing 
again,  the  weights,  as  found  in  the  first  weighing,  should  be 
placed  on  the  pan,  so  that  no  time  may  be  lost  after  the  dish 
has  been  taken  from  the  desiccator. 

272.  The  filtrate  from  the  insoluble  portion  is  analysed 
according  to  the  following  scheme  : 


Add  ammonia  and  filter. 


Precipitate  contains 
FejOg,  AiPa,  and 
P2O5.  .  Weigh, 
then  re -dissolve  in 
HCl,  and  estimate 
Fe  by  K2Cr20, 
solution  (see  para- 
graph 'J']). 


Filtrate.     Add  ammonium  oxalate.     Filter. 


Precipitate. 
Calcium 
oxalate. 
Ignite,  and 
weigh     as 
CaCO. 

Filtrate.    Add  HCl.    Boil  to  dry- 
ness.    Ignite  to  drive  off  am- 
monium    salts.       Weigh     as 
MgO,  NaCl,  and  KCl.      Dis- 
solve in  hot  water.     Filter. 

Precipitate. 
Ignite,  and 
weigh     as 
MgO. 

Filtrate.      Esti- 
mate   potassi- 
um by  PtCl4  as 
in  paragraphs 
33-36. 

The  sodium  is 
the    difFerenc 
residue  (MgC 
and     the    si 
KCl. 

estimated  here  as 
:e   between    total 
),  KCl,  and  NaCl) 
im  of  MgO   and 

M  2 


164  ^<^^^  Analysis  [273-275 


Details  of  the  Analysis 

273.  Oxide  of  Iron  and  Alumina.— Boil  the  filtrate 
from  the  insoluble  portion  over  a  Bunsen,  then  add  dilute  am- 
monia in  slight  excess.  Boil  for  a  few  seconds,  then  allow  the 
precipitate  to  settle.  Filter  rapidly,  wash  once  by  decantation, 
then  re-dissolve  in  HCl  and  re-precipitate  with  ammonia.  Boil 
again  and  filter,  collecting  the  filtrates  from  both  precipitations 
in  the  same  beaker.  Wash  well  with  hot  water,  dry,  ignite, 
and  weigh. 

The  object  of  this  double  precipitation  is  to  prevent  the 
precipitate  from  being  contaminated  with  CaCOa-  Should 
there  be  any  considerable  quantity  of  lime  in  the  soil, 
the  precipitate  first  formed  by  ammonia  is  sure  to  contain 
some. 

After  weighing  the  mixed  oxides,  dissolve  them  by  digesting 
with  a  few  c.c.  of  strong  HCl.  When  the  digestion  has  gone 
on  for  about  half-an-hour,  decant  the  liquid  into  a  250-c.c.  flask 
and  add  a  further  quantity  of  acid.  When  it  is  all  dissolved, 
make  up  to  250  c.c.  with  water.  Reduce  the  iron  in  50  c.c.  of 
this,  and  titrate  exactly  as  described  in  paragraph  77. 

The  percentage  of  Al^Og  is  obtained  by  subtracting  the 
sum  of  the  percentages  of  FegOg  and  P2O5  from  the  percentage 
of  ammonia  precipitate. 

274.  Lime. — Boil  the  filtrate  and  washings  from  the 
ammonia  precipitate,  and  add  ^  gram  of  solid  ammonium  oxalate. 
Allow  to  settle,  and  test  the  supernatant  liquid  for  lime  with 
a  drop  of  ammonium  oxalate  solution.  Should  lime  be  present 
in  the  liquid,  another  ^  gram  of  solid  oxalate  must  be  added. 
Filter.  Wash  well  with  hot  water.  Dry  the  precipitate,  ignite 
in  a  Fletcher  furnace  (see  paragraph  46),  and  weigh  as  CaO. 

275.  Magnesia    and    Alkalis.— Transfer   the   filtrate 


276-278]  Details  of  the  Analysis  165 

from  the  lime,  which  will  be  of  considerable  bulk,  to  a  weighed 
platinum  dish  3  inches  in  diameter,  and  evaporate  over  a  rose 
burner  turned  down  so  low  that  ebullition  does  not  quite  take 
place.  When  all  the  liquid  has  been  boiled  down  to  a  very 
small  bulk,  add  5  c.c.  of  strong  HCl,  and  finish  by  evaporating  to 
dryness  on  the  water  bath.  Next  place  on  an  Argand,  and  ignite 
at  a  low  temperature  so  as  to  drive  off  the  ammonium  salts. 
This  ignition  will  take  two  or  three  hours.  When  all  fuming 
ceases,  heat  to  dull  redness  in  the  Bunsen  flame  for  about  half- 
a-minute,  cool  in  a  desiccator,  and  weigh.  The  contents  of  the 
dish  are  MgO,  KCl,  and  NaCl. 

276.  Magnesia. — Dissolve  the  weighed  residue  in  hot 
water  and  filter  rapidly,  washing  with  hot  water.  Dry  the  pre- 
cipitate, ignite,  and  weigh  as  MgO. 

277.  Potash. — Add  5  c.c.  of  platinum  chloride  solution, 
evaporate  on  the  water  bath,  and  estimate  the  potash  exactly 
as  in  paragraphs  33-36. 

278.  Soda. — This,  as  stated  in  the  table,  is  calculated 
by  difference.  This  is  done  as  follows  :  Calculate  the  KoPtClg 
obtained  in  the  last  operation  as  percentage  of  the  total  weight 
of  soil  taken.  This  multiplied  by  -193  gives  percentage  of 
KgO  in  the  soil. 

Percentage  of  K2O  x  1*585  gives  percentage  of  KCl. 
Add  the  percentage  of  KCl  to  that  of  magnesia,  and  subtract 
from  the  percentage  of  alkaline  chlorides  and  magnesia.  The 
result  is  the  percentage  of  NaCl.  Multiply  the  percentage  of 
NaCl  by  -53,  and  the  result  will  be  the  percentage  of  NagO  in 
the  soil. 


1 66 


Soil  Analysis 


[279,  280 


DETERMINATIONS   MADE   IN   SEPARATE 
PORTIONS   OF  THE   SOIL 

In  addition  to  the  general  mineral  analysis  given  above, 
it  is  usual  to  determine  nitrogen^  nitrates,  chlorides^  carbonates, 
and  organic  carbon. 

279.  Nitrogen. — Weigh  out  20  grams  of  the  finely 
ground  sample  of  soil,  and  estimate  the  nitrogen  by  the  acid 
method  (paragraphs  92-95). 

280.  Nitrates  and  Chlorides.— These  two  con- 
stituents are   estimated   in   the   water  extract  of  soil.     The 

apparatus  used  for  the 
extraction  is  shown  in 
fig.  44.  A  is  the  top  of  a 
Winchester  quart  bottle 
which  has  been  cut  off 
from  the  bottom.  This 
is  connected,  by  means 
of  a  piece  of  glass 
tubing  and  two  well- 
fitting  corks,  with  the 
stout  tabulated  flask  b. 


Fig.  44. 


This  apparatus  is  connected  first  with  the  safety  bottle  c,  then 
with  the  pump  d.  Inside  a  is  placed  a  disc  of  copper  gauze 
2  inches  in  diameter;  this  covers  the  aperture  of  the  neck,  and 
serves  as  support  for  a  piece  of  filter  paper.  By  means  of  this 
apparatus  the  whole  of  the  nitrates  and  chlorides  in  500  grams 
of  soil  may  be  extracted  with  100  c.c.  of  water. 

Weigh  out  500  grams  of  the  original  sample  (undried)  of 
the  soil,  and  place  it  over  the  filter  paper  in  a  (fig.  44).  If  it 
be  of  a  loose  texture,  press  it  down  well ;  then  pour  50  c.c.  of 
distilled^water  over  it.     After  it  has  stood  five  minutes,  set  the 


281-284]  Determinations  in  Separate  Portions  of  Soil  167 

pump  going  and  allow  the  water  to  run  through.  Now  add 
another  50  c.c,  and  allow  the  pump  to  continue  working  until 
water  ceases  to  drop  into  b.  The  liquid  is  then  ready  for 
further  treatment. 

281.  Nitrates. — Pour  the  extract  obtained  as  described 
in  the  last  paragraph  into  a  platinum  dish.  Wash  the  flask 
twice,  and  add  the  washings  to  the  rest  of  the  liquid.  Evapo- 
rate over  the  water  bath  until  only  about  5  c.c.  is  left.  Wash 
this  liquid  with  a  little  hot  water  into  Schloesing's  nitrate 
apparatus  (fig.  31),  and  determine  the  nitrogen  exactly  as 
described  in  paragraph  107. 

282.  Chlorine. — Extract  another  portion  of  the  soil  in 
exactly  the  same  manner,  and  estimate  the  chlorine  with  stan- 
dard AgNOg  solution  as  described  in  paragraph  69. 

283.  Carbonates.— Estimate  the  CO2  by  one  of  the 
methods  described  in  paragraphs  48-53.  The  quantity  of  soil 
to  be  used  in  this  operation  varies  according  to  the  nature  of 
the  soil.  About  5  grams  will  generally  be  found  convenient, 
but  should  large  quantities  of  lime  or  magnesia  be  found  in  the 
earlier  part  of  the  analysis,  a  smaller  quantity  of  the  soil  will 
be  required.  On  the  other  hand,  soils  very  poor  in  lime  and 
magnesia  are  correspondingly  poor  in  carbonic  acid. 

284.  Organic  Carbon. — The  organic  portion  of  a  soil 
generally  goes  by  the  name  of  'humus,'  and  this  humus  is 
usually  found  to  contain  58  per  cent,  of  carbon.  If,  therefore, 
we  estimate  the  carbon,  we  are  able  to  calculate  the  quantity  of 
humus  ;  and  seeing  that  we  have  in  a  previous  part  of  the 
analysis  estimated  the  loss  on  burning,  we  can  calculate,  by 
difference,  the  percentage  of  combined  water  in  the  soil.  The 
determination  of  carbon  is  conducted  as  follows :  Fit  up  an 
apparatus  similar  to  the  one  described  in  paragraph  55  and 
shown  in  fig.  22,  the  only  difference  to  be  made  being  the 
omission  of  the  pipette  ^,  for  which  is  substituted  an  ordinary 


1 68  Soil.  Analysis  [285 

straight  glass  tube  with  a  piece-  of  india-rubber  tubing  and  a 
soda  lime  tube   attached   in   the   same  manner  as  shown  in 

fig.   2  2. 

Weigh  out  from  2  to  8  grams  of  the  soil,  according  to  its 
nature,  into  the  flask,  and  add  first  20  c.c.  of  water,  then  30  c.c. 
of  strong  sulphuric  acid.  Now  connect  the  flask  directly  with  the 
aspirator,  so  that  the  CO2  formed  in  the  flask  by  decomposition 
of  the  carbonates  may  be  drawn  ofl".  Whilst  this  is  proceeding, 
weigh  the  U  tube  (/  fig,  22),  and  place  all  the  tubes  together. 
Next  connect  up  the  apparatus  as  shown  in  the  figure.  Take 
the  cork  out  of  the  flask,  and  introduce  8  grams  of  coarsely 
powdered  pure  potassic  dichromate.  Close  the  flask  again,  and 
heat  gently  as  long  as  gas  is  evolved;  then  heat  nearly  to 
boiling  for  some  time.  Finally,  aspirate  air  through  the  appa- 
ratus for  about  ten  minutes.  Detach  the  weighed  U  tube, 
allow  it  to  cool,  and  weigh  again.  The  increase  of  weight  is 
due  to  the  CO2  formed  from  the  oxidation  of  the  humus.  If 
this  amount  of  CO2  be  multiplied  by  -471,  the  weight  of  humus 
is  obtained. 


ANALYSIS   OF  THE   PORTION   INSOLUBLE   IN 
HYDROCHLORIC   ACID 

The  actual  analysis  of  this  portion  of  the  soil  is  exactly 
similar  to  the  analysis  of  the  soluble  portion,  the  only  difficulty 
being  to  get  it  into  solution.  This  is  accomplished  by  one  of 
three  methods. 

285.  The  Sulphuric  Acid  Method.— Weigh  out  roughly 
2  grams  of  the  insoluble  portion  of  the  soil  in  a  weighed  plati- 
num dish.  Ignite  over  an  Argand,  allow  to  cool  in  a  desic- 
cator, and  weigh  accurately.  Add  10  c.c.  of  strong  sulphuric 
acid,  and  heat  on  an  Argand  very  cautiously.  This  operation 
must  be  carried  on  in  a  draught  cupboard,  as  the  heating  has 


286,  287]    Portion  Insoluble  in  Hydrochloric  Acid       i6g 

to  be  continued  until  nearly  all  the  acid  has  been  volatilised. 
When  the  capsule  is  nearly  dry,  allow  it  to  cool,  dilute  with 
water  acidulated  with  hydrochloric  acid,  filter,  wash  thoroughly, 
dry,  ignite,  and  weigh.  The  residue  consists  of  sand  and 
amorphous  silica.  The  silica  which  results  from  the  decom- 
position of  the  clay  may  be  dissolved  out  with  strong  sodium 
carbonate  solution,  and  the  residue  weighed  again  as  sand. 
The  filtrate  is  analysed  as  described  in  paragraph  272. 

286.  Hydrofluoric  Acid  Method. — This  method  de- 
pends upon  the  fact  that  when  hydrofluoric  acid  acts  upon 
silica  a  gaseous  product  is  formed  according  to  the  equation 

Si02  +  4HF  =  2H20  +  SiF4. 

Thus  all  the  silica  will  pass  off  in  the  course  of  evaporation. 

Weigh  out  about  2  grams  of  the  soil  in  a  platinum  dish, 
ignite,  and  weigh  accurately  as  described  in  paragraph  285. 
Now  add  concentrated  HF  until  the  substance  is  just  covered. 
Digest  on  the  water  bath  for  an  hour,  then  add  another  portion 
of  the  acid,  and  digest  again  for  half-an-hour.  Now  add  2  c.c. 
of  sulphuric  acid  (equal  parts  acid  and  water),  and  heat  up 
gradually  over  an  Argand.  The  heating  must  be  continued 
until  the  acid  fumes  cease  to  come  off.  Allow  the  residue  to 
cool,  and  treat  with  20  c  c.  of  strong  HCl.  Allow  to  stand  on 
the  water  bath  for  half-an-hour,  then  dilute.  A  clear  solution 
should  be  obtained.  Should  any  insoluble  matter  be  present, 
decant  the  liquor  into  a  beaker,  and  treat  with  HF  again. 

The  liquid  eventually  obtained  may  be  analysed  according 
to  the  table  shown  in  paragraph  272,  the  silica  being  estimated 
by  difference. 

287.  The  Fusion  Method.— For  this  method  two 
portions  must  be  used,  one  of  which  is  fused  with  a  mixture  of 
potassic  and  sodic  carbonates,  which  form  alkaline  silicates  and 
so   render  the  substance  soluble;   whilst  the  other  is  heated 


170  Soil  Analysis  [288,  289 

with  calcic  carbonate  and  ammonium  chloride,  which  break 
down  the  insoluble  silicates  and  set  free  the  alkalis  in  the  form 
of  alkaline  chlorides. 


Fusion  with  Alkaline  Carbonates 

288.  Preparation  of  Fusion  Mixture. — This  mixture  of 
Na2C03  and  K2CO3  in  molecular  proportions  may  be  pre- 
pared either  by  mixing  in  a  mortar  10  grams  of  sodium  carbon- 
ate and  1 3  grams  of  potassium  carbonate,  both  of  which  have 
been  recently  fused,  or  by  igniting  Rochelle  salt  in  a  platinum 
dish,  extracting  the  charred  mass  with  water,  and  evaporating 
the  liquid  to  dryness. 

In  any  case  the  mixture  must  be  dried  perfectly  before 
using. 

289.  The  Operation. — Weigh  out  about  a  gram  of 
the  substance  in  a  platinum  dish,  ignite,  and  weigh  again  (para- 
graph 285).  Weigh  out  roughly  5  gmmsoi dry  fusion  mixture 
into  a  deep  platinum  crucible.  Pour  the  weighed  quantity  of 
'  insoluble  matter '  on  top  of  the  fusion  mixture,  sweeping  in 
the  last  portions  with  a  small  camel's-hair  brush.  Now  stir  up 
all  the  contents  of  the  crucible  with  a  stout  piece  of  copper 
wire  until  they  are  fairly  mixed.  Brush  back  into  the  crucible 
any  traces  which  may  adhere  to  the  wire.  Place  the  cover 
loosely  on  top  of  the  crucible,  and  heat  it  on  a  pipe-clay  triangle 
over  a  Bunsen  burner  until  the  whole  mass  is  fused.  Continue 
this  heating  until  effervescence  becomes  subdued,  then  transfer 
the  crucible  to  a  Fletcher  muffle  furnace  (fig.  17),  and  keep  at 
a  bright-red  heat  for  forty  minutes.  Allow  it  to  cool  just  below 
redness,  then  cool  rapidly  by  placing  on  a  cold  iron  plate. 
This  will  induce  the  vitrified  mass  to  become  very  brittle. 
When  quite  cool,  place  the  crucible  at  the  bottom  of  a  12-oz. 
beaker,  covered  by  a  clock  glass,  and  from  a  wash  bottle  fill  the 


290,  291]         Fusion  with  Alkaline  Carbonates  171 

crucible  with  hydrochloric  acid  (equal  parts  acid  and  water). 
When  effervescence  has  ceased,  turn  the  beaker  so  as  to  lay  the 
crucible  on  its  side,  and  add  more  acid  until  the  crucible  is 
quite  free  from  solid  matter.  Next  remove  the  crucible  with  a 
glass  rod  and  wash  it  thoroughly  with  hot  water,  adding  the 
washings  to  the  acid  solution. 

All  the  silica  in  the  portion  of  soil  taken  will  be  in  the 
gelatinous  hydrated  state.  The  liquid  must  be  evaporated  to 
dryness  on  the  water  bath,  then  heated  on  the  sand  bath  to 
render  all  silica  insoluble.  A  few  c.c.  of  strong  HCl  must  be 
added,  to  moisten  the  whole  mass,  and  then  50  c.c.  of  weak 
acid.  After  evaporating  to  about  half  bulk  on  the  water  bath, 
the  silica  must  be  filtered  off,  dried,  ignited,  and  weighed,  and 
the  filtrate  must  be  analysed  according  to  the  table  in  para- 
graph 272. 

DETERMINATION   OF   'INSOLUBLE'  ALKALIS 

290.  Preparation  of  Pure  Calcic  Carbonate. — Dissolve 
Iceland  spar  or  good  marble  in  the  least  possible  quantity  of 
HCl,  add  lime  water  until  just  alkaline,  boil,  and  filter.  Raise 
the  clear  filtrate  to  the  boiling-point,  and  add  pure  ammonium 
carbonate  in  excess.  Allow  to  settle,  wash  thoroughly  by 
decantation,  transfer  to  a  platinum  dish,  and  dry  first  in  the 
steam  oven,  then  at  a  low  temperature  over  an  Argand  burner. 

291.  Preparation  of  Pure  Ammonium  Chloride. — The 
great  dif^culty  in  performing  the  operation  to  be  described 
with  commercial  ammonium  chloride  is  that  the  crystals  are  so 
tough  and  wiry  as  to  render  powdering  well  nigh  impossible. 
This  difficulty  may  be  overcome  by  dissolving  pure  NH4CI  of 
commerce  in  the  smallest  quantity  of  hot  water,  filtering,  and 
evaporating  until  the  salt  begins  to  crystallise.  If  it  be  now 
cooled   down   rapidly  by  circulating   cold   water  around   the 


72 


Soil  Analysis 


[292 


vessel  in  which  it  is  contained,  and  vigorously  stirred,  the 
ammonium  chloride  will  crystallise  out  in  minute  crystals. 
These  may  be  filtered  off  and  dried.  The  result  will  be  a  fine 
powder  just  suitable  for  our  purpose. 

292.  The  Operation. — Weigh  out  about  a  gram  of  the 
dry  substance,  as  described  in  paragraph  285,  and  introduce 

it  into  a  deep  platinum 
crucible,  together  with 
a  gram  of  dry  NH4CI 
and  6  grams  of  pure 
dry  CaCOa.  Mix  tho- 
roughly with  a  stout 
wire,  brushing  back  all 
adherent  matter  from 
the  wire  to  the  crucible. 
Cover  the  crucible,  and 
raise  it  to  a  red  heat 
over  a  Bunsen  for  an 
hour.  The  heating  is 
best  started  by  plac- 
ing the  crucible  in  an 
inclined  position  (see 
fig.  45)  and  heating  the  top  of  the  crucible  first,  moving  the 
burner  from  time  to  time  until  the  whole  is  at  a  red  heat.  At 
the  end  of  an  hour  place  the  crucible  in  a  Fletcher  muffle 
furnace  (fig.  17),  and  keep  at  a  bright  red  heat  for  forty 
minutes. 

Allow  the  crucible  to  cool.  Place  in  a  12-oz.  beaker  and 
slake  the  contents  with  hot  water.  They  will  rapidly  break 
up,  and  may  be  detached  from  the  crucible  with  a  wash  bottle. 
Remove  the  crucible  with  a  glass  rod  and  wash  well,  adding 
the  washings  to  the  liquid  in  the  beaker.  Boil  the  liquid  for 
a  few  minutes.     Decant  through  a  filter.     Wash  three  times 


Fig.  45. 


293] 


Determination  of  ^ Insoluble*  Alkalis 


173 


by  decantation,  using  50  c.c.  of  water  for  each  washing  ;  then 
wash  once  with  hot  water  on  the  filter. 

The  filtrate  will  contain  all  the  alkalis  in  the  form  of 
chlorides,  together  with  some  calcic  chloride  and  calcic  hydrate. 
Precipitate  the  lime  by  adding  ammonium  carbonate  solution 
in  excess,  together  with  a  little  ammonia  and  ammonium 
oxalate.  Boil  well  and  filter,  washing  by  decantation.  Evapo- 
rate the  filtrate  to  dryness  in  a  large  platinum  dish,  and  ignite 
gently  to  drive  off  all  ammoniacal  compounds.  Weigh  as 
NaCl  +  KCl,  and  proceed  as  described  in  paragraphs  277  and 
278. 

ANALYSIS   OF   LIMESTONES 

There  is  very  little  difference  in  the  general  method 
adopted  between  the  analysis  of  limestones  and  the  analysis  of 
the  '  soluble  '  portion  of  soils,  though  it  is  not  often  necessary 
to  determine  any  other  constituents  in  a  limestone  than  the 
silicates,  the  lime,  and  the  magnesia. 

293.  General  Table. 


Dissolve  in  HCl,  and  evaporate  to  dryness ;  dissolve  in  water,  and  filter. 


Precipitate. 
Dry  and 
weigh  as 
insoluble 
silicates 
and  sand. 


Filtrate.  Treat  with  ammonia,  filter,  dissolve  precipi- 
tate in  HCl,  and  re-precipitate  ;  add  both  filtrates 
together. 


Precipitate. 
Weigh  as 
Fe^Oa,  A1,0„ 
and  P2O5. 
Dissolve  up 
and  esti- 

mate ^-fi^-, 
as  in  refuse 
manure. 


Filtrate. 
filter. 


Add  HA,  then  (NHJ,  Ox  ; 


Precipitate. 
Burn    and 
weigh     as 
CaCO,. 


Filtrate.  Evaporate 
with  HNO3.  Add 
microcosmic  salt  to 
boiling  solution;  cool, 
and  render  ammoni- 
acal. Weigh  precipi- 
tate as  MgjPaO,. 


174  ^^^^  Analysis  [294-296 


Details   of  the   Analysis 

294.  Silicates. — Weigh  out  about  i  gram  of  the  air-dried 
substance;  dissolve  in  HCl,  as  described  in  paragraph  10,  and 
evaporate  to  dryness  on  the  water  bath.  When  quite  dry,  heat 
on  the  sand  bath  for  a  few  minutes.  Allow  to  cool,  and 
moisten  with  2  c.c.  of  strong  HCl.  Stir  to  break  up  clots. 
Add  25  c.c.  of  dilute  HCl  (1-3),  evaporate  for  five  minutes, 
then  filter.  Wash  thoroughly  with  hot  water,  transfer  the 
precipitate  to  a  weighed  platinum  dish,  ignite,  and  weigh. 

295.  Iron  Oxide  and  Alumina.— The  estimation  of 
oxide  of  iron  and  alumina  is  complicated  by  the  presence  of 
the  large  excess  of  lime  salts  in  the  liquid.  When  ammonia  is 
added  a  considerable  quantity  of  CaCO.}  will  be  precipitated, 
together  with  the  hydrated  oxides. 

Raise  the  filtrate  from  the  silicates  to  boiling-point,  remove 
from  the  flame,  and  add  dilute  ammonia  until  just  alkaline. 
Boil  again,  and  allow  the  precipitate  to  settle.  Decant  off  the 
liquid  through  a  filter.  Wash  once  by  decantation ;  then  re- 
dissolve  in  dilute  HCl,  as  described  in  paragraph  273.  Boil, 
and  re-precipitate  with  ammonia.  Should  the  precipitate  now 
be  small  (only  a  few  milligrams)  it  may  be  weighed,  but 
usually  it  should  be  dissolved  and  re-precipitated  a  third  time. 

After  igniting  and  weighing,  the  precipitate  should  be  dis- 
solved and  tested  for  P2O5,  according  to  the  method  described 
in  paragraph  239.     Should  it  be  present,  it  must  be  estimated. 

296.  Lime. — In  a  good  agricultural  limestone  there  is 
little  difficulty  about  this  estimation,  which  is  carried  out  as 
described  in  paragraph  274.  In  dolomitic  limestones,  how- 
ever, it  is  more  difficult.  When  magnesic  salts  are  present 
and  a  large  excess  of  ammonium  oxalate  is  used,  the  calcic 
oxalate    precipitate   is   largely    contaminated    with    magnesic 


297,  298]  Analysis  of  Limestones  175 

oxalate.  On  the  other  hand,  should  only  just  sufficient  of  the 
ammonium  salt  be  added,  the  MgCl2  present  has  a  distinct 
solvent  action  on  the  calcium  oxalate.  The  most  simple  way 
of  overcoming  this  difficulty  is  by  dissolving  and  re-precipitating, 
though  it  may  be  remarked  that  less  magnesia  is  precipitated 
in  the  presence  of  acetic  acid  than  in  the  presence  of  free 
ammonia. 

To  the  total  filtrates  add  acetic  acid  until  slightly  acid; 
boil,  and  add  \\  gram  of  pure  ammonium  oxalate.  Allow  to 
settle,  and  decant  through  a  filter.  Wash  once  by  decantation, 
and  dissolve  in  the  smallest  possible  quantity  of  dilute  HCl. 
Add  ammonia  until  only  slightly  acid ;  boil,  and  add  ammo- 
nium acetate  solution  in  excess.  Allow  to  settle,  and  filter, 
washing  four  times  by  decantation.     Weigh  as  CaCOg. 

297.  Magnesia. — The  filtrates  from  the  two  lime  filtra- 
tions  will  not  only  consist  of  a  large  bulk  of  liquid,  but  will 
contain  great  quantities  of  ammonium  salts.  It  is  therefore 
well  to  evaporate  the  liquid  to  smaller  bulk.  This  is  readily 
done  by  placing  in  a  large  wide-mouthed  beaker  over  a  Bunsen 
burner,  keeping  the  liquid  at  such  a  temperature  that  it  only 
just  boils,  and  adding  sufficient  liquid  from  time  to  time  to 
keep  it  about  a  quarter  full.  To  the  first  lot  of  liquid  add 
5  c.c.  of  strong  nitric  acid,  and  as  more  liquid  is  added  to  replace 
what  is  evaporated,  add  more  acid,  5  c.c.  at  a  time,  until  20  c.c. 
has  been  used.  This  will  decompose  the  ammonium  salts, 
which  will  first  form  ammonium  nitrate,  then  nitrous  oxide  and 
water.  When  all  the  liquid  has  been  concentrated  to  about 
200  c.c,  add  to  the  hot  solution  2  grams  of  pure  microcosmic 
salt,  stirring  until  quite  dissolved.  Allow  to  cool,  and  render 
strongly  ammoniacal.  Stir,  and  allow  to  stand  for  one  and 
a-half  hour.  Filter,  dry,  ignite,  and  weigh  as  Mg2P207  (using 
the  precautions  described  in  paragraph  40). 

298.  Calculation.  —  It   is   not    usual    to   estimate    the 


1/6 


Soil  Analysis 


[299 


CO2  in  limestones,  as  this  may  be  calculated  from  the  per- 
centages of  lime  and  magnesia,  and  the  analysis  is  stated  as 
follows  : 


Combined  water,  alkalis,  &c. 

CaCOg      . 

MgC03     .         . 

FcjO,  and  AI2O3 

PP3         .        . 

Silicates    . 


Nottinehamshire 
dolomite 


5-34 

54-54 

38-35 

•48 

•08 

I -21 


100  •00 


Derbyshire 
mountain  limestone 


•22 

97-35 

71 
•09 

1-63 


lOO'OO 


ANALYSIS   OF   LIME 

299.  This  analysis  is  carried  out  in  exactly  the  same  way 
as  the  analysis  of  limestone,  except  that  it  is  usual  to  estimate 
the  CO2  and  the  combined  water  present.  The  CO2  may  be 
estimated   by   one   of  the   methods   described  in  paragraphs 

50-56. 

Combined  Water.  Weigh  out  about  2  grams  of  the  lime 
into  a  platinum  dish,  and  place  in  a  Fletcher  muffle  furnace 
(fig.  17),  heated  to  a  bright  red  for  twenty  minutes.  Allow 
to  cool  to  a  dull  red;  remove  to  a  desiccator,  allow  to  cool 
thoroughly,  and  weigh.  The  loss  of  weight  represents  the 
quantity  of  CO2  and  combined  water  present.  By  subtracting 
CO2  we  obtain  the  amount  of  water  combined  with  the  CaO 
in  the  form  of  Ca(H0)2. 


ANALYSIS   OF  GAS   LIME 

The  only  difference  between  this  and  the  analysis  of 
lime  is  that  in  gas  lime  the  sulphur  must  be  estimated.  Now, 
this  sulphur  exists  in  three  forms — viz.,  sulphate  of  calcium, 
sulphite  of  calcium,  and  sulphide  of  calcium.     It  is  usual  to 


300,  301]  Analysis  of  Gas  Lime  177 

estimate  the  total  sulphur  and  the  sulphur  in  the  form  of  calcic 
sulphate.     The  '  sulphite  '  sulphur  is  less  frequently  estimated. 

300.  Total  Sulphur. — Weigh  out  2  grams  of  the  gas 
lime;  transfer  to  a  12-oz.  conical  flask;  add  5  grams  KCIO3; 
place  a  funnel  in  the  neck  to  prevent  loss  by  spirting,  and 
pour  in  50  c.c.  pure  HNO3.  When  the  reaction  moderates  in 
violence  transfer  to  a  water  bath,  and  heat  until  CI  ceases  to 
be  evolved ;  this  will  take  about  an  hour.  Transfer  to  a  wide- 
mouthed  beaker,  washing  the  flask  thoroughly  with  hot  water ; 
add  20  c.c  strong  HCl,  and  evaporate  to  dryness.  Heat  for  a 
minute  on  the  sand  bath.  Cool,  and  moisten  with  2  c.c.  strong 
HCl.  Add  100  c.c.  H2O.  Stir  well,  and  allow  to  stand  for 
twenty  minutes.  This  operation  will  oxidise  all  the  sulphur  to 
sulphuric  acid,  so  that  it  will  all  be  in  the  form  of  CaS04. 
Filter,  and  wash  the  precipitate  with  warm  dilute  HCl  (1-20) 
to  dissolve  any  traces  of  CaS04  left  behind. 

The  next  process  is  to  remove  the  excess  of  lime,  which 
would  interfere  with  the  subsequent  precipitation.  Render  the 
solution  just  ammoniacal,  and  add  ammonium  carbonate  solution 
in  excess.  Allow  to  settle,  and  decant  through  a  filter.  Wash  by 
decantation  with  hot  water.  To  the  filtrate  add  HCl  cautiously 
until  effervescence  ceases  ;  then  expel  the  dissolved  CO2  by 
heating  for  a  short  time  on  the  water  bath.  Raise  to  a  boil, 
add  boiling  BaCl2  solution,  and  proceed  to  the  estimation  of 
BaS04  as  described  in  paragraphs  28-31.  The  percentage  of 
sulphur  must  be  calculated  from  the  percentage  of  BaS04. 

301.  Sulphur  as  Calcic  Sulphate.— Weigh  out  2  grams, 
dissolve  in  HCl,  and  separate  the  silicates  as  described  in 
paragraph  271.  Next  separate  the  lime,  and  determine  the 
SO3  present  exactly  as  described  in  the  last  paragraph.  The 
HCl  will  expel  all  sulphites  and  sulphides  as  SO2  and  Hj,S 
respectively,  and  only  the  sulphur  originally  in  the  state  of 
calcic  sulphate  will  be  precipitated  as  barium  sulphate. 

N 


[302 


PART   VIII 

ANAL  YSIS  OF  DAIR  V  PROD UCE 

MILK   ANALYSIS 

Milk  is  an  exceedingly  complex  substance.  To  separate 
and  estimate  its  various  component  parts  entails  a  long  and 
difficult  series  of  operations.  In  practice,  however,  it  is  found 
sufficient  to  make  the  following  determinations  : 

Specific  gravity ; 

Fat ; 

Total  solids ; 

Ash. 

Sometimes  this  analysis  is  carried  out  with  the  object  of 
discovering  whether  the  milk  has  been  diluted  with  water  or 
reduced  in  quality  by  the  removal  of  cream  ;  but  the  true  com- 
mercial analysis  is  directed  towards  discovering  the  value  of 
the  milk  for  dairy  purposes.  Thus  the  chemist  of  the  Aylesbury 
Dairy  Company  analyses  over  ten  thousand  samples  yearly,  not 
to  detect  fraud,  but  to  see  that  the  milk  supplied  to  the  public 
reaches  a  certain  standard  of  richness. 

302.  Specific  Gravity. — This  is  very  readily  determined 
by  means  of  a  hydrometer  such  as  is  used  for  taking  the  S.G. 
of  turnip  juice.  The  lactometer  is  a  modified  form  of  hydro- 
meter, marked  off  in  degrees.  A  difference  of  one  degree 
represents  a  difference  in  specific  gravity  of  'ooi.     The  gradu- 


302]  Milk  Analysis  1 79 

ation  generally  begins  at  15°  (S.G.=  1-015),  ^^d  ends  at  45° 

(S.G.  =  ro45). 

To  use  this  instrument,  pour  just  as  much  milk  as  will  con- 
veniently fill  tl^e  lactometer  cylinder  into  a  flask  and  insert  a 
thermometer.  Should  the  temperature  be  60°  F.,  or  15°  C,  the 
S.G.  may  at  once  be  taken.  Should  the  temperature,  how- 
ever, be  different,  it  must  be  brought  to  60°  F.  by  immersing 
the  flask  in  warm  or  cold  water  until  the  thermometer  registers 
the  right  temperature. 

Pour  the  milk  into  the  cylinder,  and  lower  the  lactometer 
carefully  into  the  liquid.  Note  the  graduation  at  the  top  of 
the  meniscus. 

The  specific  gravity  of  pure  milk  is  from  30°  to  34° 
of  the  lactometer  (S.G.  =  1*030  to  i'034);  the  addition  of 
10  per  cent,  of  water  lowers  the  reading  to  27°  to  30°,  or  about 
three  degrees. 

A  difficulty  here  arises,  seeing  that  the  removal  of  cream 
increases  the  density  of  milk  to  about  33°  to  37°  ;  hence  the  lacto- 
meter cannot  be  relied  upon  without  some  method  of  finding 
out  whether  we  are  dealing  with  skim  milk  or  whole  milk. 
This  is  provided  in  the  creamometer,  which  usually  consists 
of  an  ordinary  stoppered  graduated  cylinder  of  100  c.c. 
capacity. 

Fill  the  cylinder  up  to  the  loo-c.c.  mark  with  milk,  and 
allow  to  stand  twenty-four  hours.  The  cream  will  then  have 
risen  to  the  top,  and  its  volume  may  be  read  off. 

Pure  whole  milk  should  give  at  least  10  c.c  cream. 

A  rough  estimate  of  the  amount  of  water  added  may  be 
obtained  from  using  the  creamometer  and  lactometer  con- 
jointly. 

Very  many  conditions,  however,  affect  the  specific  gravity 
of  milk.  When  it  is  freshly  drawn  from  the  cow  not  only  is  it 
warm,  but  as  a  rule  it  contains  a  considerable  quantity  of  air  in 

N  2 


l8o  The  Analysis  of  Dairy  Produce  [303 

solution,  so  that  its  specific  gravity  is  lower  at  the  instant  of 
drawing  than  four  or  five  hours  later. 

Allowing  for  this  source  of  error,  there  is  a  very  definite 
relationship  between  the  specific  gravity  ar^  the  chemical 
contents  of  the  milk.  Qualitatively,  an  increase  in  the  fat  or 
cream  lessens  the  specific  gravity,  whilst  an  increase  in  the 
solids  not  fat  renders  the  specific  gravity  higher. 

Quantitatively  this  variation  of  the  specific  gravity  has 
been  used  to  check  the  accuracy  oi  analysis,  and  also  to 
give  a  rapid  and  fairly  accurate  estimate  of  the  percentage 
of  fat. 

It  will  be  seen  from  the  later  paragraphs  in  this  chapter 
that  the  estimation  of  fat  is  the  most  difficult  operation  in  the 
commercial  analysis  of  milk;  if,  therefore,  the  exceedingly  simple 
operations  of  estimating  the  total  solids  (paragraph  303)  and 
the  specific  gravity  will  give  a  correct  idea  of  the  percentage  of 
fat,  much  work  may  be  saved. 

Richmond's  formula  is  as  follows  : 

F=o-859T-o-2i86G, 

where  F  represents  the  percentage  of  fat,  T  the  percent- 
age of  total  solids,  and  G  is  the  lactometer  degree  {i.e.,  the 
number  by  which  the  specific  gravity  of  the  milk  exceeds  that 
of  water  (water  =  I'ooo). 

This  formula  is  based  on  the  fact,  first  worked  out  by 
Clausnizer  and  Mayer,  that  every  addition  of  i  per  cent,  of  fat 
decreases  the  specific  gravity  of  milk  by  'ooi,  whilst  every 
addition  of  i  per  cent,  of  solids  not  fat  increases  the  specific 
gravity  by  -00375. 

303.  Total  Solids. — Measure  out  accurately  into  a 
weighed  platinum  dish  25  c.c.  of  milk  which  has  been  well 
shaken  up  ;  add  two  drops  of  strong  acetic  acid,  and  evaporate 
to  dryness  on  the  water  bath.     Transfer  to  the  steam  oven,  and 


304-306]  Milk  Analysis  i8l 

heat  until  the  weight  is  constant.  The  final  weight,  minus  the 
weight  of  the  dish,  gives  the  weight  of  total  solids. 

The  acetic  acid  added  curdles  the  milk,  and  prevents  the 
formation  of  a  scum  which  would  retard  the  evaporation. 

Fat. — This  is  the  most  important  determination,  and 
several  methods  are  in  use.  The  first  of  these  is  the  most 
reliable. 

304.  Adams  Process. — A  known  weight  of  milk  is 
absorbed  by  a  roll  of  filter  paper.  The  paper  is  then  dried 
and  extracted  with  ether. 

This  method  is  the  standard  one  in  use  by  most  analysts. 

The  roll  of  filter  paper  is  prepared  as  follows  :  Cut  a  strip 
of  white  filter  paper  22^  inches  long  and  2 J  inches  wide. 
Place  it  on  a  table,  and  lay  along  its  surface  a  piece  of  string 
with  one  end  just  reaching  to  the  end  of  the  strip  and  the 
other  end  projecting  about  6  inches  beyond  the  paper.  Now 
roll  paper  and  string  into  a  coil.  The  string  will  prevent  the 
successive  coils  from  touching  one  another.  Tie  the  free 
end  round  the  coil,  so  as  to  keep  the  paper  permanently  in 
position. 

305.  Purification  of  the  Paper. — Fat-free  paper  may 
be  purchased,  but  ordinary  paper  may  be  rendered  practically 
free  by  extraction  for  i^  hour  in  the  Soxhlet  apparatus. 
If  many  determinations  be  required,  it  is  best  to  soak  a 
number  of  the  strips  in  several  changes  of  rectified  spirit  con- 
taining 10  per  cent,  glacial  acetic  acid.  The  paper  should 
stand  at  least  two  hours  in  this  solution. 

306.  The  Determination. — Suspend  the  roll  of  paper 
from  a  glass  rod  by  means  of  the  free  end  of  the  string.  Shake 
up  the  sample  of  milk,  and  draw  off  5  c.c.  with  a  pipette. 
Allow  it  to  run  from  the  end  of  the  pipette  on  to  the  roll, 
which  will  completely  absorb  it.  Suspend  the  roll  in  the  steam 
oven  for  about  an  hour  to  dry ;  then  place  it  in  the  Soxhlet 


1 82  The  Analysis  of  Dairy  Produce         [307,  308 

apparatus  (fig.  38),  and  extract  with  ether  for  i^  hour. 
Transfer  the  fat  to  a  beaker,  and  weigh  exactly  as  described  in 
paragraph  142. 

307.  Rapid  Methods. — Of  late  years  several  forms  of 
apparatus  have  been  introduced  which  estimate  the  amount  of 
fat  in  milk  both  rapidly  and  accurately.  These  may  be  divided 
into  three  classes,  'the  gravimetric,'  the  * areometric,'  and  the 
'  centrifugal.'  In  the  areometric  and  gravimetric  methods  a 
certain  quantity  of  ether  is  mixed  with  a  certain  quantity  of 
milk,  and  then  allowed  to  separate.  The  percentage  of  fat  is 
deduced  either  from  the  specific  gravity  of  the  ether,  or  by 
evaporating  an  aliquot  portion  of  the  ether  and  weighing.  In 
the  centrifugal  methods  the  milk  is  first  acted  upon  by  some 
reagent  which  will  dissolve  the  casein,  then  the  fat  is  separated 
by  centrifugal  force.  One  form  of  each  of  these  three  methods 
is  given  below. 

The  Werner  Schmidt  Method 

In  this  method  the  casein,  &c.,  are  dissolved  by  boiling  with 
hydrochloric  acid.  This  leaves  a  brown  solution  from  which 
the  fat  may  be  easily  extracted  by  shaking  with  ether.  The 
percentage  of  fat  in  the  ether  is  estimated  by  evaporating  a 
portion  and  weighing  the  dry  residue. 

308.  The  Process. — A  Werner  Schmidt  tube  is  a  stoppered 
test  tube  of  70  or  80  c.c.  capacity;  it  has  a  mark  to  indicate 
when  it  contains  10  c.c.  of  liquid  and  another  to  indicate  20  c.c. 
Above  the  20-c.c.  mark  are  accurate  graduations  for  every 
o*i  C.C.  up  to  50  c.c. 

Ten  c.c.  of  the  well  mixed  milk  is  poured  into  this  tube, 
then  10  c.c.  of  strong  hydrochloric  acid  is  added.  The 
mixture  is  well  shaken,  then  boiled  for  a  few  minutes  over  a 
Bunsen.      The   liquid   will  then   be   clear   but  deep   brown. 


309,  310]  The   Werner  Schmidt  Method  183 

Some  analysts  prefer  to  heat  the  tube  in  a  water  bath,  but  this 
is  a  slow  process,  and  as  the  only  object  of  this  method  is  to 
obtain  a  rapid  result  with  fair  accuracy,  it  is  best  to  proceed  as 
quickly  as  possible. 

When"  the  liquid  is  quite  free  from  clots  it  is  cooled  down, 
and  the  tube  filled  up  to  the  50-c.c.  mark  with  ether.  The 
tube  is  corked  up,  well  shaken,  and  allowed  to  stand  until  the 
ethereal  layer  has  completely  separated. 

Ten  c.c.  of  this  ethereal  extract  is  measured  off  into  a 
weighed  dish,  evaporated  to  dryness,  and  weighed.  The  result, 
after  subtracting  the  weight  of  the  dish,  will  be  one-fifth  of  the 
weight  of  fat  in  10  c.c.  of  milk.  Knowing  the  specific  gravity 
of  the  milk,  it  is  easy  to  calculate  the  percentage  of  fat. 

Soxhlet's  Areometric  Method 

309.  Apparatus. — The  apparatus,  which  is  shown  in 
fig.  46,  consists  of  a  bottle  in  which  the  solution  of  the  fat  takes 
place,  and  a  tube  surrounded  by  a  water  jacket  and  enclosing  a 
delicate  hydrometer  giving  specific  gravities  from  743  to  766. 
Attached  to  the  hydrometer  is  a  thermometer.  The  bottle 
may  be  connected  with  the  water-jacketed  tube  by  inserting  an 
india-rubber  stopper  through  which  pass  two  tubes  arranged 
as  for  a  wash  bottle,  the  delivery  tube  being  attached  to  the 
apparatus  whilst  the  blowing  tube  has  an  india-rubber  blower 
fixed  to  it.  This  apparatus  is  complete  for  one  determination. 
Should  a  large  number  be  required  in  rapid  succession,  a  large 
number  of  bottles  will  be  required. 

310.  The  Operation. — Measure  out  200  c.c.  of  milk  into 
one  of  the  bottles;  add  10  c.c.  of  caustic  potash  solution 
(the  solution  used  for  expelling  ammonia  after  heating  with 
H2SO4  in  the  acid  process  of  nitrogen  estimation,  paragraph 
91,  may  be  used)  and  60  c.c.  of  ether.     The  ether  must  be 


1 84 


The  Analysis  of  Dairy  Produce 


[311 


Table  for  Soxhlet's  Areometric  Method  of  Milk  Fat 

Estimation. 


Specific 
gravity 

Fat 
per  cent. 

Specific 
gravity 

Fat 
per  cent. 

Specific 
gravity 

Fat 
per  cent. 

43 

2-07 

45 '9 

2-39 

48-8 

274 

43-1 

2-o8 

46 

2-40 

48-9 

275 

43-2 

2 '09 

46-1 

2-42 

49 

276 

43-3 

2-IO 

46-2 

2-43 

49 -I 

277 

43 -4 

2-II 

46-3 

2 '44 

49-2 

278 

43*5 

2*12 

46-4 

2-45 

49 -3 

279 

43*6 

2-13 

46-5 

2-46 

49 -4 

2 -80 

437 

2-14 

46-6 

2-47 

49-5 

2-8i 

43-8 

2-i6 

467 

2-49 

49*6 

2-83 

43'9 

2-17 

46-8 

2-50 

497 

2-84 

44 

2-i8 

46-9 

2-51 

49-8 

2-86 

44-1 

2-19 

47 

2-52 

49-9 

2-87 

44 '2 

2 '20 

47-1 

2-54 

50 

2-88 

44*3 

2-22 

47-2 

2-55 

50-I 

2-90 

44 '4 

2-23 

47-3 

2-56 

50-2 

2-91 

44-5 

2-24 

47 '4 

2-57 

50-3 

2-92 

44-6 

2-25 

47*5 

2-58 

50*4 

2*93 

447 

2-26 

47-6 

2 -60 

50-5 

2-94 

44-8 

2-27 

477 

2-6i 

50-6 

2-96 

44 '9 

2-28 

47-8 

2-62 

507 

2-97 

45 

2-30 

47-9 

2-63 

50-8 

2-98 

45-1 

2-31 

48 

2-64 

50-9 

2-99 

45-2 

2-32 

48-1 

2-66 

51 

3-00 

45-3 

2'33 

48-2 

2-67 

51-1 

3-OI 

45-4 

2*34 

48-3 

2-68 

51-2 

3-03 

45-5 

2-35 

48-4 

270 

51-3 

3-04 

45*6 

2.36 

48-5 

271 

51-4 

3-05 

457 

2-37 

48-6 

272 

51-5 

3-06 

45-8 

2-38 

487 

273 

51-6 

3-o8 

Specific 
gravity 


517 

51-8 

51-9 

52 

52-1 

52-2 

52-3 

52-4 

52-5 

52-6 

527 
52-8 

52-9 

53 

53'i 

53-2 

53-3 

53*4 

53*5 

53-6 

537 

53-8 

53*9 

54 

54*1 

54*2 

54*3 

54*4 

54*5 


311] 


Soxhlet's  Areometric  Method 


1 8s 


Table  for  Soxhlet's  Areometric  Method  of  Milk  Fat 
Estimation— continued. 


Specific 
gravity 

Fat 
per  cent. 

Specific 
gravity 

Fat 
per  cent. 

Specific 
gravity 

Fat 
per  cent. 

Specific 
gravity 

Fat 
per  cent. 

54-6 

3-45 

57-5 

3-82 

60-4 

4-23 

63-3 

4-67 

547 

3-46 

57-6 

3-84 

6o-5 

4-24 

63-4 

4-69 

54-8 

3-47 

577 

3-85 

6o-6 

4-26 

63-5 

470 

54-9 

3-48 

57-8 

3-87 

607 

4-27 

63-6 

471 

55 

3-49 

57-9 

3-88 

6o-8 

4*29 

637 

473 

55-1 

3-51 

58 

3-90 

60-9 

4-30 

63-8 

475 

55-2 

3-52 

58-1 

3-91 

61 

4-32 

63-9 

477 

55-3 

3-53 

58-2 

3-92 

6i-i 

4-33 

64 

479 

55-4 

3-55 

58'3 

3-93 

61 -2 

4-35 

64-1 

4-8o 

55-5 

3-56 

58-4 

3-95 

61-3 

4-36 

64-2 

4-82 

55-6 

3 '57 

58-5 

3-96 

61-4 

4-37 

64-3 

4-84 

557 

3 '59 

58-6 

3-98 

61-5 

4-39 

64-4 

4-85 

55-8 

3-60 

587 

3*99 

61 -6 

4-40 

64-5 

4-87 

55-9 

3-6i 

58-8 

4-01 

617 

4-42 

64-6 

4-88 

56 

3-63 

58-9 

4 -02 

6i-8 

4  "44 

647 

4-90 

56-1 

3-64 

59 

4-03 

61-9 

4-46 

64-8 

4-92 

56-2 

3-65 

59-1 

4-04 

62 

4*47 

64-9 

4*93 

56-3 

3-67 

59-2 

4-06 

62-1 

4-48 

65 

4-95 

56-4 

3-68 

59-3 

4-07 

62-2 

4-50 

65-1 

4*97 

56-5 

3-69 

59-4 

4-09 

62-3 

4-52 

65-2 

4-98 

56-6 

371 

59-5 

4-II 

62-4 

4*53 

65-3 

5-00 

567 

372 

59-6 

4-12 

62-5 

4-55 

65-4 

5-02 

56-8 

373 

597 

4-14 

62-6 

4-56 

65-5 

5-04 

56-9 

374 

59-8 

415 

627 

4-58 

65-6 

5-05 

57 

375 

59-9 

4-i6 

62-8 

4-59 

657 

5 -07 

57-1 

376 

60 

4-i8 

62-9 

4-61 

65-8 

5-09 

57-2 

378 

6o-i 

4-19 

63 

4-63 

65-9 

5-II 

57-3 

3-80 

6o-2 

4 -20 

63-1 

4-64 

66 

5-12 

57-4 

3-8i 

6o-3 

4-21 

63-2 

4-66 

1 86 


The  Analysis  of  Dairy  Produce 


[310 


saturated  with  water  by  shaking  up  equal  quantities  of  ether 
and  water  in  a  Winchester  and  allowing  to  stand  over  night. 
A  stopper  is  placed  in  the  bottle,  and  it  is  shaken  vigorously 
for  half-a-minute,  then  it  is  placed  in  a  vessel  of  water  kept 
at  a  temperature  of  between  17°  and  18°  C,  shaking  gently 
from  time  to  time.     The  ethereal  solution  of  fat  will  rise  to  the 


Fig.  46. 

surface.  When  the  bottle,  with  its  contents,  has  attained  the 
temperature  of  the  water,  the  stopper  is  removed,  and  the 
india-rubber  stopper  shown  in  the  figure  is  introduced.  The 
longer  glass  tube  is  adjusted  so  that  it  terminates  inside  the 
ether  layer.  By  opening  the  clip  and  gently  pressing  the 
blowing  bulb,  the  ethereal  solution  is  passed  up  into  the  water- 


311,  312]  Soxhlefs  Areometric  Method  187 

jacketed  tube,  which  is  surrounded  by  water  at  from  17°  to 
18°  C.  Here  it  rises  until  the  hydrometer  floats.  The  clip  is 
now  tightened  up,  and  the  graduation  where  the  lower  surface 
of  the  meniscus  crosses  the  stem  of  the  hydrometer  is  read  off. 
The  temperature  is  also  taken. 

311.  Calculation. — Very  frequently  the  graduation  on  the 
hydrometer  omits  the  first  decimal  place,  which  is  always  7. 
Thus  the  numbers  would  be  set  down  from  43  to  66,  meaning 
from  743  to  '766.  If  the  temperature  be  exactly  i7'5,  then 
the  percentage  of  fat  may  be  read  off  by  reference  to  the  table. 
Should  the  temperature  be  different,  a  correction  must  be 
applied.  This  is  done  by  adding  or  subtracting  the  number 
of  degrees  above  or  below  17*5  from  the  third  place  of 
decimals  in  the  specific  gravity.  (This  is  the  unit  place  in  the 
graduation.)  Thus,  supposing  that  the  reading  of  the  hydro- 
meter is  53'5,  and  the  temperature  19-2,  the  difference  of  the 
temperature  from  17-5  is  17,  and  the  specific  gravity  of  the 
solution  is  7535.  If  we  add  on  the  number  of  degrees 
difference  to  the  third  place  of  decimals,  we  get  7552  ;  or  if 
we  add  it  to  the  units  place  of  the  graduation,  we  get  55*2; 
and  on  reference  to  our  table  we  find  that  this  represents  3*52 
per  cent,  of  fat  (for  table  see  pages  184  and  185). 

Babcock's  Centrifugal  Method. 

312.  Apparatus. — The  special  apparatus  required  for  this 
method  is,  firstly,  a  centrifugal  machine,  and,  secondly,  separat- 
ing bottles.  The  machines  in  use  are  very  various  in  structure, 
but  the  most  common  form  is  shown  in  fig.  47.  The  one  thing 
essential  to  the  proper  working  of  the  method  is  that  the  bottles 
may  be  whirled  round  at  a  rate  of  not  less  than  600  revolutions 
per  minute.  Any  machine  which  will  do  this  may  be  used. 
The  bottles  are  made  to  hold  40  to  45  c.c.   of  milk,  and  the 


1 88 


The  Analysis  of  Dairy  Produce        [313,  314 


necks    are   long   and   graduated,   each   division   representing 
•04  c.c. 

313.  The  Operation. — Measure  out  18  c.c.  of  milk  into 
one  of  the  bottles,  and  add  17*5  c.c.  of  sulphuric  acid  (S.G.  i"82). 
The  liquid  will  become  hot  and  dark  in  colour.  Place  the 
bottle  in  the  machine,  and  turn  it  at  as  high  a  speed  as  possible 
for  six  or  seven  minutes.  It  is  best  to  whirl  the  bottles  directly 
after  adding  the  acid,  otherwise  they  may  cool  down  and  require 


Fig.  47. 


heating  again  to  get  the  fat  in  a  liquid  condition.  As  soon 
as  the  bottles  have  been  sufficiently  whirled,  fill  them  up  to  the 
base  of  the  neck  with  hot  water.  Whirl  them  again  for  about 
two  minutes,  add  more  hot  water  to  the  top  of  the 
graduations,  and  whirl  for  a  minute  more.  Stand  the  bottles 
upright  in  water  kept  at  55°  C.  for  a  few  minutes,  and  read  off 
the  volume  of  fat. 

314.  Calculation. — Each  division  of  '04  c.c.  is  equal  to 
•2  per  cent,  of  fat  if  exactly  18  c.c.  of  milk  be  used  and  the 


315]  Babcock's  Centrifugal  Method  189 

temperature  be  55°  C.  At  this  temperature  the  specific  gravity 
of  fat  is  -9. 

A  small  correction  should  be  made  for  the  specific  gravity 
of  the  milk,  but  it  is  customary,  when  testing  milk,  to  have  a 
pipette  graduated  to  hold  exactly  18  c.c.  of  milk  of  normal 
density — viz.,  i"03. 

315.  Remarks  on  the  Results  of  Milk  Analysis. — The  two 
methods  used  in  tampering  with  milk  are  the  addition  of  water 
and  the  removal  of  cream.  In  calculating  the  extent  to  which 
either  of  these  operations  has  been  carried  on,  the  analyst 
assumes  the  milk  to  be  of  the  lowest  probable  quality  before 
adulteration,  and  states  his  results  calculated  on  this  assump- 
tion as  '  minimum  '  adulteration.  The  minimum  standard  for 
pure  milk  is  generally  agreed  upon  as  9  per  cent.  '  solids  not 
fat '  and  3  per  cent,  fat,  though  the  '  Somerset  House '  standard 
is  rather  lower.  ^  To  calculate  added  water ^  let  a  be  the  per- 
centage of  soHds  not  fat.  Then  the  percentage  of  added 
water  will  be  at  least 

looa 
100 . 

9 

To  calculate  the  percentage  of  fat  removed  from  milk  which 
has  been  skimmed,  let  a  be  the  percentage  of  solids  not  fat  and 
d  the  percentage  of  fat ;  then  the  minimum  amount  of  fat 
removed  from  100  parts  of  the  original  milk 

=  3_  _  ^  parts. 
9 

'  The  introduction  of  the  '  Adams '  process  gave  rather  higher  per- 
centages of  fat  than  had  been  obtained  before.  Hence  the  percentage  of 
'  solids  not  fat '  became  lower.  The  '  Somerset  House '  analysts  apparently 
accept  the  lowered  value  of  8-5  instead  of  9*0  for  the  '  solids  not  fat.' 


I90  The  Analysis  of  Dairy  Produce        [316-319 


BUTTER   ANALYSIS 

In  the  ordinary  commercial  analysis  of  butter,  estimations 
are  made  of  water ^fat^  curd^  and  salt^  though  as  a  rule  the  fat 
is  estimated  by  difference.  When  the  presence  of  foreign  fat — 
i.e.^  fat  not  derived  from  milk — is  suspected,  the  fat  undergoes 
further  manipulation. 

316.  Water. — Five  grams  are  weighed  out  in  a  flat 
porcelain  dish  of  the  same  shape  and  size  as  that  used  for  the 
determination  of  '  total  solids '  in  milk.  The  dish  is  placed 
in  a  steam  oven  until  all  the  globules  of  water  which  gather 
beneath  the  fat  on  melting  have  disappeared.  The  dish  is  then 
re-weighed.     The  loss  is  taken  as  water. 

317.  A  rapid  method  which,  in  skilful  hands,  gives  good 
results  is  performed  by  placing  the  dish  with  the  weighed 
quantity  on  a  sand  bath,  and  stirring  constantly  with  a  short 
glass  rod  which  has  been  weighed  with  the  dish.  By  holding 
a  perfectly  clean  polished  watch  glass  over  the  hot  fat  from 
time  to  time,  it  can  be  seen  whether  steam  is  rising  from  the 
dish,  as  steam  will  dim  the  surface  of  the  glass.  The  operation 
only  takes  a  very  few  minutes. 

318.  Curd. — Mix  the  dry  fat  from  the  last  operation  with 
about  10  c.c.  of  ether.  Filter  the  liquid  so  formed  either 
through  a  weighed  filter  or,  better,  through  counterpoised 
filters,  such  as  are  used  in  the  determination  of  potassium 
described  in  paragraph  34. 

Wash  the  filter  and  its  contents  with  ether  until,  on  evapor- 
ating a  drop  of  the  filtrate,  no  residue  is  left.  Dry  the  filter  in 
a  water  bath,  and  weigh.     The  weight  gives  curd  plus  ash. 

319.  Ash. — Transfer  the  filter  paper  containing  the  curd 
and  ash  to  a  weighed  platinum  dish  and  ignite  over  an  Argand 
at  the  temperature  used  in  the  determination  of  CaCOa  (see 


320,  321] 


Butter  Analysis 


191 


paragraph  45).  When  the  ash  is  quite  white,  weigh  the  dish 
again.  By  subtracting  the  weight  of  ash  from  the  weight  of  curd 
plus  ash  obtained  in  the  last  experiment,  the  weight  of  curd 
is  found.  Of  course  it  must  be  remembered  that  the  weight 
of  the  ash  from  the  filter  has  to  be  subtracted  from  the  total 
ash. 

Generally  speaking,  almost  the  whole  of  the  ash  is  salt. 
This  may,  however,  be  determined  by  dissolving  in  water  and 
estimating  the  chlorine  with  standard  AgNOg  solution,  as 
described  in  paragraph  69. 

320.  Enter  the  results  as  follows  : 


I 

11 

III 

Water     .        .        . 
Curd       .        .        . 
*Ash 
Fat.        .        .        . 

10-15 

•65 

1-97 

87-23 

9*53 

•47 

2-i6 

87-84 

1 1 -2 

3-1 

2-0 
837 

100 -oo                100 -oo 

loo-o 

♦Containing  salt      . 

I -61 

1-93          Not  determined 

Estimation   of   Foreign   Fats   in   Butter 

321.  Butter  Fat. — All  pure  fats  are  compounds  of  the 
trihydric  alcohol  glycerin  with  monobasic  organic  acids.  As 
glycerin  is  always  present,  the  identification  of  any  fat  depends 
on  the  identification  of  the  acid  which  it  contains.  Unfortu- 
nately for  the  analyst,  there  are  very  many  of  these  so-called 
'  fatty '  acids  which  resemble  one  another  so  closely  as  to  make 
their  separation  a  matter  of  great  difficulty.  Another  difficulty 
arises  from  the  fact  that  pure  fats  are  seldom  or  never  found 
in  nature.  In  the  investigation,  therefore,  of  such  natural  fats 
as  '  butter  fat '  or  '  margarine,'  experiments  must  be  made  on 
the  mixed  compounds  of  glycerin  and  a  number  of  fatty  acids. 


192  The  Analysis  of  Dairy  Produce  [322 

Milk  fat  differs  from  all  other  natural  fats  in  that  it  contains 
a  considerable  percentage  of  the  so-called  '  lower '  fatty  acids — 
i.e.^  acids  having  a  comparatively  small  molecular  weight. 
Many  of  these  lower  acids  are  volatile  at  the  temperature  of 
boiling  water,  and  are  soluble  in  water. 

These  three  properties — i.e.^  low  molecular  weight,  volatility 
in  steam,  and  solubility  in  water — are  used  for  the  detection 
and  estimation  of  those  fats  peculiar  to  butter. 

322.  Koettstorfer's  Method. — The  molecular  weight  of 
any  acid  may  be  determined  by  weighing  the  quantity  which  will 
combine  with  56  grams  of  KHO.  As  it  would  be  unscientific 
and  inconvenient  to  speak  of  the  average  molecular  weight  of 
the  fatty  acids  in  butter,  it  is  usual  to  express  this  peculiar 
property  as  a  Koettstorfer  number,  which  is  the  number  of 
milligrams  of  KHO  which  are  neutralised  by  the  fatty  acids  in 
I  gram  of  butter  fat.  In  this  method  a  weighed  quantity 
of  butter  fat  is  heated  with  an  excess  of  standard  alcoholic 
potash.  After  the  reaction  is  complete,  the  excess  of  potash 
is  estimated  by  means  of  standard  hydrochloric  acid. 

The  solutions  required  are  seminormal  hydrochloric  acid, 
which  may  be  prepared  by  one  of  the  methods  given  in  Part  II., 
and  alcoholic  potassium  hydrate. 

Alcoholic  Caustic  Potash.  Thirty-two  grams  of  caustic 
potash  are  weighed  out  roughly  and  dissolved  in  a  litre  of 
strong  alcohol.  This  solution,  if  made  from  methylated  spirit, 
very  rapidly  discolours  and  alters  in  strength.  Students  are 
advised  to  make  up  only  small  quantities  as  they  may  be 
required.  In  laboratories  where  large  numbers  of  butter 
samples  are  analysed  the  alcohol  is  specially  prepared.  Fifty 
grams  of  potash  are  dissolved  in  a  '  Winchester  '  of  methylated 
spirit  and  left  to  stand  for  at  least  a  week.  The  spirit  is  then 
distilled.  After  this  treatment  it  may  be  used  for  making 
solutions  of  caustic  alkalis,  which  will  only  alter  very  slowly. 


823]  Estimation  of  Foreign  Fats  in  Butter  193 

Melt  up  about  10  grams  of  butter  in  a  beaker  and  filter 
it.  The  easiest  way  of  doing  this  is  to  place  a  filter  funnel 
with  a  short  stem  in  the  mouth  of  a  4-oz.  conical  flask,  place 
a  paper  in  the  funnel,  and  keep  the  whole  arrangement  in 
a  steam  oven  whilst  the  filtration  proceeds.  The  fat  is  thus 
kept  fused,  so  that  it  runs  through  the  filter,  leaving  the  curd, 
salt,  and  moisture  behind. 

Weigh  out  accurately  about  2  grams  of  the  butter  fat  thus 
prepared  in  an  8-oz.  flask  of  the  shape  shown  in  fig.  11. 
Add  exactly  25  c.c.  of  the  alcoholic  potassium  hydrate,  and 
warm  on  a  water  bath,  shaking  occasionally  until  saponifica- 
tion is  complete.  Oily  drops  will  remain  on  the  surface  of  the 
liquid  until  the  reaction  is  ended.  Whilst  this  is  going  on, 
measure  out  another  25  c.c.  of  the  alcoholic  potash  into  a 
clean  flask.  Add  a  drop  of  phenol-phthalein  solution  and 
titrate  with  the  seminormal  acid. 

When  the  butter  fat  is  completely  dissolved,  add  a  drop  of 
phenol-phthalein  and  run  in  the  seminormal  acid  until  the  red 
colour  just  disappears.  Less  acid  will  be  required  in  this  case, 
as  some  of  the  potash  will  have  been  neutralised  by  the  '  fatty 
acids.' 

323.  Calculation. — From  the  first  titration  one  can 
calculate  the  weight  of  potash  in  each  c.c.  of  the  alcoholic 
potash  solution.  By  subtracting  the  volume  of  acid  required 
after  heating  with  butter  fat  from  the  volume  required  for 
the  25  c.c.  of  original  alcoholic  potash,  we  may  calculate  the 
quantity  of  alkali  used  by  the  butter.  Knowing  the  weight  of 
butter  fat  used  in  the  experiment,  it  is  easy  to  find  the  number 
of  milligrams  of  potash  required  by  each  gram  of  butter.  A 
concrete  example  will  make  this  plain : 

Weight  of  butter  fat  =  2*193  ; 

N 
25  c.c.  alcoholic  KHO  required  22-1     -  HCl ; 


194  ^-^^  Analysis  of  Dairy  Produce  [324 

25  c.c.  alcoholic  KHO  after  saponification  required 

4-2  ^HCl; 

N 
I  c.c.  —  HCl  neutralises  '028  gram  KHO  ; 

.*.  Amount  of  alkali  used  =  (22-1  —  4-2)  x  '028 

=  17*9  X  28  =  501 '2  milligrams. 

501*2 
This  divided  by  weight  of  fat  =  =228*1. 

J        t,  2*193 

The  Koettstorfer  number  for  pure  butter  fat  varies  from 
221*5  to  233,  averaging  227*25.  The  number  given  by  oleo- 
margarine is  about  195*5.  ^^  ^^  example  just  quoted,  the 
material  was  pure  butter  fat.  Had  the  number  fallen  below  222 
or  223,  it  would  have  been  viewed  with  suspicion,  whilst 
had  it  fallen  below  221*5  it  would  certainly  have  been  adulte- 
rated. 

An  approximate  idea  of  the  percentage  of  foreign  fat  may 
be  obtained  from  the  formula  : 

(227*25  —  n)  X  3-17, 

where  n  is  the  Koettstorfer  number  found  by  experiment. 

Should  the  number  indicate  that  the  butter  has  been  adul- 
terated, it  is  advisable  to  use  one  of  the  more  definte  methods 
described  below. 

324.  Hehner's  Process. — Weigh  out  about  4  grams  of  the 
butter  fat  so  obtained  in  a  tared  8-oz.  conical  flask ;  add  10  c.c. 
of  saturated  alcoholic  potash.  Heat  gently  on  the  water  bath, 
shaking  from  time  to  time,  until  the  whole  of  the  fat  has  turned 
into  a  soap.  The  end  of  the  reaction  is  easily  seen  from  the 
fact  that  the  unsaponified  fat  floats  as  a  yellow  oily  drop  on 
the  surface  of  the  liquid.  This  drop  gradually  diminishes, 
and  finally  disappears.  When  the  saponification  is  complete, 
dilute  with  50  c.c  of  water  and  allow  the  alcohol  entirely  to 


325]  Estimation  of  Foreign  Fats  in  Butter  195 

evaporate  on  the  water  bath.  Now  pour  the  contents  of  the 
flask  into  a  separating  funnel  (preferably  made  of  thin  glass, 
see  fig.  48).  Wash  the  flask  well  with  hot  water,  and  add  the 
washings.  Whilst  the  liquid  in  the  separating 
funnel  is  still  hot,  add  hot  dilute  hydrochloric 
acid  (1-3)  until  the  liquid  is  acid.  Shake  well, 
and  allow  to  stand  over  night.  This  will  separate 
all  the  fatty  acids,  which  will  collect  in  a  wax-like 
film  above  the  water.  This  long  standing  is 
necessary  to  allow  the  complete  separation  of  the 
insoluble  acids,  which,  when  once  thoroughly  col- 
lected on  the  surface  of  the  water,  give  no  trouble 
in  the  subsequent  washings.  When  the  separation  has  taken 
place,  shake  the  apparatus  to  detach  the  film  from  the  walls  of 
the  bulb,  and  run  off"  the  liquid  by  means  of  the  stopcock 
below.  Now  pour  about  50  c.c.  of  boiling  water  into  the  bulb, 
and  shake  to  wash  the  fatty  acids.  They  will  melt  and  rapidly 
collect  on  the  surface  of  the  water,  which  will  be  left  perfectly 
clear,  and  may  be  run  off.  This  washing  must  be  repeated 
several  times  until  the  whole  of  the  washing  liquid,  together 
with  the  original  acid  liquor,  measures  300  c.c.  In  the  final 
washing  run  off  the  water  as  completely  as  possible,  then  run 
the  acids  into  a  tared  shallow  dish.  Wash  out  the  acids  which 
adhere  to  the  funnel  with  a  little  ether.  Place  the  dish,  with  its 
contents,  in  the  water  bath,  and  heat  until  it  ceases  to  lose  weight. 
325.  Calculation. — All  animal  fats  contain  about  95*5 
per  cent,  of  insoluble  fatty  acids.  Butter  fat  contains  on  the 
average  87*5  per  cent.  It  is,  therefore,  easy  to  calculate  the 
approximate  percentage  of  foreign  fat  in  a  sample  of  butter  by 

the  formula 

^  =  i2'5  {a  —  87-5), 

where  x  =  percentage  of  foreign  fat  and  a  =  percentage  of 
insoluble  fatty  acids  found. 

o  2 


196  The  Analysis  of  Dairy  Produce  [326 

The  working  out  of  this  formula  is  as  follows  : 
The  difference  between  the  percentage  of  these  acids  in 
butter  fat  and  in  animal  fat  is  95*5  —  87*5  =  8. 

It  is,  therefore,  on  this  8  per  cent,  that  we  must  base  our 
calculation. 

If  an  excess  of  8  %  (over  87'5  %)  means  100  %  foreign  fatf 
then      „        „i%  „  „      ^-^% 

5>  11     ^^     /O  >>  J)  -— ^ /o  ,, 

Supposing  that  we  have  found  a  per  cent,  insoluble  fatty 
acids;  then 

N  =  («  -  87-5), 

.*.   the  percentage  of  foreign  fat  present  =  —      q  •> 

which  equals  12*5  (^  —  87 '5). 

326.  Reichert  Meisl  Method.— It  was  stated  in  para- 
graph 321  that  butter  fat  differed  from  most  other  natural  fats, 
in  that  it  contained  a  certain  quantity  of  volatile  fatty  acids. 
This  quantity  is  usually  stated  as  the  nujjiber  of  c.c.  of 
decitiormal  alkali  (barium  hydrate)  required  to  neutralise  the 
volatile  acids  in  5  grams  of  fat.  The  fat  is  first  saponified  by 
heating  with  a  solution  of  soda  in  glycerin,  then  the  acids  are 
set  free  by  dilute  sulphuric  acid,  and  the  volatile  portion  is 
distilled  oif.  The  acidity  of  the  distillate  is  estimated  by 
means  of  standard  barium  hydrate.  The  solutions  required 
are  : 

Caustic  Soda  Solution.  Fifty  grams  of  caustic  soda  is 
dissolved  in  a  small  quantity  of  water  and  the  solution 
diluted  to  100  c.c.  It  is  then  mixed  with  500  grams  of  pure 
glycerin. 

Dilute  Sulphuric  Acid.  The  ordinary  dilute  sulphuric  acid 
must  be  diluted  until  5  c.c.  just  neutralises  2  c.c.  of  the  glycerin- 
caustic-soda  solution. 


327,  328]     Estimation  of  Foreign  Fats  in  Butter  197 

Decinormal  Baryta  Solution.  This  must  be  prepared  by 
dissolving  about  18  grams  Ba(0H)2  in  a  litre  of  water,  and 
standardising  with  decinormal  sulphuric  acid  as  described  in 
paragraph  64. 

327.  The  Process. — Five  grams  of  the  butter  fat  is  weighed 
in  an  8-oz.  conical  flask;  10  c.c.  of  the  glycerin  solution  is 
added,  and  the  mixture  is  heated  on  a  wire  gauze  until  it  ceases 
frothing,  and  the  solution  becomes  clear.  It  is  then  allowed 
to  cool,  and  5  c.c.  of  freshly  boiled  distilled  water  is  added. 
When  solution  is  complete,  50  c.c.  of  the  sulphuric  acid  is 
poured  in,  and  the  flask  at  once  attached  to  a  condenser.  It 
is  as  well  to  place  a  piece  of  pumice  or  a  piece  of  clay 
pipe-stem  in  the  liquid,  as  it  is  apt  to  '  bump '  during  the 
distillation.  The  flask  is  now  heated  until  no  c.c.  of  the 
distillate  has  been  collected.  This  must  be  filtered  through  a 
dry  filter  paper  into  a  loo-c.c.  flask. 

The  100  c.c.  thus  collected  is  titrated  with  the  decinormal 
baryta. 

328.  Calculation. — Add  one  tenth  to  the  number  of  c.c 
of  baryta  used.  If  exactly  5  grams  of  fat  has  been  weighed 
out,  at  least  26  c.c.  of  baryta  should  be  required.  Other  fats 
give  very  small  quantities  of  volatile  acid,  using  about  half  a  c.c. 
of  decinormal  baryta.  This  method  is  therefore  the  most 
useful  and  definite  one  when  the  percentage  of  foreign  fat  is 
to  be  determined. 

Remarks  on  the  Results  of  Butter  Analysis. — The  water  in 
butter  should  not  exceed  12  per  cent.  The  curd  and  salt 
together  should  be  less  than  8  per  cent.  The  curd  should 
not  exceed  4  per  cent. 

The  keeping  power  of  a  butter  depends  on  several  circum- 
stances, such  as  its  general  condition,  but  a  butter  containing 
large  quantities  of  nitrogenous  matter  (curd)  will  turn  rancid 


198  The  Analysis  of  Dairy  Produce         [329-333 

sooner,  all  other  conditions  being  equal,  than  one  containing 
smaller  quantities. 

The  fat  should  not  fall  below  80  per  cent. 


CHEESE   ANALYSIS 

The  determinations  ordinarily  made  in  cheese  analysis  are 
water ^  fat ^  casein  {nitrogenous  matter)^  and  ash. 

329.  Water. — Grate  a  piece  a  cheese  on  a  bread  grater 
until  a  sufficient  quantity  of  gratings  has  been  collected,  then 
weigh  out  5  grams  of  the  material  in  a  dish,  and  heat  in  the 
steam  oven  until  no  further  loss  takes  place.  Loss  of  weight 
=  moisture. 

330.  Fat.— This  is  estimated  in  Soxhlet's  apparatus  as 
shown  in  fig.  38  and  described  in  paragraph  140,  but  the  special 
precaution  is  necessary  that  the  cheese  must  be  quite  dry. 
The  best  method  is  to  use  the  portion  in  which  the  moisture 
has  been  determined,  removing  it  completely  from  the  drying 
dish  to  a  cartridge  case  of  filter  paper,  and  extracting  as  usual. 

331.  Casein.— Usually  estimated  by  difference.  Should 
a  direct  determination  be  necessary,  it  may  be  made  by  esti- 
mating the  nitrogen  by  the  acid  process  (paragraphs  92-95)  in 
about  half  a  gram  of  the  cheese,  and  multiplying  the  percentage 
of  nitrogen  by  6*25. 

332.  Ash  may  most  easily  be  determined  in  the  portion 
which  has  been  extracted,  or  5  grams  may  be  weighed  into  a 
platinum  dish,  and  burned  over  an  Argand  at  as  low  a  tempera- 
ture as  possible. 

The  salt  may  be  determined  by  dissolving  the  ash  and 
titrating  with  decinormal  AgNOa- 

The  phosphates  may  be  determined  by  the  method 
described  in  paragraph  246, 

333.  Adulteration  of  Cheese.— Margarine  is. frequently 


333]  Cheese  Analysis  199 

added  to  cheese  made  from  poor  milk.  This  may  be  deter- 
mined by  examining  a  portion  of  the  fat  in  the  manner 
described  for  the  determination  of  foreign  fats  in  butter. 

Cheese  is  occasionally  coloured  with  chromate  of  lead  or 
salts  of  copper.  These  may  be  tested  for  in  the  ash  by  any 
qualitative  method. 


[334-336 


PART    IX 
WATER  ANALYSIS 

334.  It  is  not  very  often  that  the  agriculturar  analyst  is 
called  upon  to  analyse  water.  In  this  chapter,  therefore,  only 
that  part  of  water  analysis  which  is  most  useful  is  described. 
For  information  on  such  subjects  as  the  analysis  of  gases  con- 
tained in  water,  and  the  combustion  method  of  analysing  the 
solid  matters,  students  are  referred  to  larger  text  books. 

335.  In  the  statement  of  results  two  methods  are  at  present 
in  vogue.  Some  chemists  state  the  number  of  grains  of  each 
substance  contained  in  a  gallon  of  water,  considering  a  gallon 
of  water  to  weigh  70,000  grains.  Others  state  their  results  in 
parts  per  100,000  of  the  water.  In  this  chapter  all  results  are 
worked  out  in  grains  per  gallon.  Parts  per  100,000  may  be 
calculated  by  dividing  the  grains  per  gallon  by  7. 

ANALYSIS  OF  WATER  FOR  DRINKING  PURPOSES 

336.  Before  proceeding  to  the  analysis  proper,  notes  should 
be  taken  as  to  the  colour,  taste,  and  smell  of  the  water. 

The  colour  is  best  seen  by  filling  a  tall  narrow  glass  cylinder, 
free  from  colour,  with  the  water,  placing  it  on  a  white  tile,  and 
looking  down  through  it. 

The  taste  and  smell  are  best  noted  when  the  sample  is 
slightly  warmed. 


337-339]  Analysis  of  Water  for  Drinking  Purposes  201 

337-  Estimation  of  Suspended  Matter.  —  This 
operation  is  unnecessary  unless  the  water  be  distinctly  turbid. 

Wash  a  6-inch  disc  of  filter  paper  with  distilled  water  free 
from  ammonia.  When  about  2  litres  has  passed  through,  test 
the  last  portion  for  ammonia  by  Nessler's  test  (see  page  203). 
If  the  water  has  ceased  to  dissolve  ammonia,  dry  the  paper  in 
the  air  oven  at  100°  C.  until  it  is  of  constant  weight. 

Shake  up  the  sample  of  water,  measure  out  2  litres,  and  filter 
through  the  prepared  paper.  Collect  the  filtrate  in  a  clean 
bottle  (Winchester  quart).  Next  wash  thoroughly  with  distilled 
water,  rejecting  the  washings,  and  dry  in  the  air  bath,  as  before, 
until  it  ceases  to  lose  weight.  The  weight  of  suspended 
matter  in  2  litres  of  the  water  is  thus  found.  Calculate  this 
into  grains  per  gallon. 

Next,  cutting  up  the  filter,  place  in  a  weighed  platinum  dish, 
and  ignite  over  an  Argand  until  all  carbonaceous  matter  is 
driven  off.  Cool  in  a  desiccator,  and  weigh.  On  subtracting 
the  weight  of  the  dish  and  the  filter  ash,  we  obtain  the  weight 
of  inorganic  suspended  matter  in  2  litres  of  the  water. 

338.  Microscopic  Examination.— In  cases  where  sus- 
pended matter  is  present  it  is  usual  to  make  a  microscopic 
examination.  In  this  case  a  quantity  of  the  water  is  left  in 
a  tall  cylinder,  and  the  undissolved  matter  allowed  to  settle. 
The  supernatant  water  is  carefully  poured  off,  and  the  mud 
at  the  bottom  placed  on  a  slip  of  glass  and  examined  by  the 
microscope.  For  information  as  to  the  microscopic  appear- 
ance of  sediments,  see  Hassal's  '  Food  and  its  Adulterations.' 

339.  Total  Solids  in  Solution.— Should  the  water  have 
been  filtered,  this  estimation  is  made  in  the  filtered  portion. 

Measure  out  500  c.c.  of  the  water  in  a  graduated  flask,  and 
fill  an  accurately  tared  platinum  evaporating  basin  about  half 
full  of  water  from  the  flask.  The  water  may  be  evaporated 
over  a  water  bath,  or,  better,  over  a  rose  burner  protected  by 


202  Water  Analysis  [340 

a  lamp  screen,  as  shown  in  fig.  49.  The  burner  must  be  turned 
down  as  low  as  possible.  The  water  will  then  evaporate  slowly 
and  without  ebullition.  As  it  evapo- 
rates it  must  be  filled  from  time  to 
time  until  the  whole  500  c.c.  has  been 
placed  in  the  basin.  The  evaporation 
is  now  carried  on  until  only  about 
20  c.c.  is  left  in  the  dish.  Then  remove 
the  dish  to  a  water  bath  until  appar- 
ently dry.  When  no  further  evapora- 
'^*  '^^'  tion  takes  place,  heat  in  the  air  bath  at 

1 10°  C.  until  its  weight  is  constant.    The  residue,  after  weighing, 
must  be  saved  for  the  nitrate  estimation. 

340.  Estimation  of  Nitrogenous  Matter.— The 
nitrogen  present  in  water  may  be  in  one  or  both  of  two  forms 
known  respectively  as  '  free  ammonia '  and  '  albuminoid  am- 
monia ' — the  free  ammonia  being  either  ammonia  or  ammoniacal 
salts,  and  the  albuminoid  ammonia  being  obtained  from  the 
organic  nitrogen. 

For  the  estimation  of  these  two  constituents  the  following 
solutions  are  necessary : 

Nessler^s  Solution.  Dissolve  16*5  grams  of  potassic  iodide 
and  6  "5  grams  of  mercuric  chloride  in  400  c.c.  of  ammonia- 
free  water.  Boil  and  stir  until  all  is  dissolved.  Now  add 
cold  saturated  solution  of  mercuric  chloride  until  the  precipi- 
tate of  mercuric  iodide  just  becomes  permanent.  Now  add 
80  grams  of  caustic  potash  or  60  grams  of  caustic  soda, 
allow  to  cool,  and  dilute  to  500  c.c.  Finally,  to  ensure  sensi- 
tiveness, add  a  few  more  drops  of  mercuric  chloride  solution, 
and  allow  the  precipitate  to  settle.  This  solution  is  kept  in  a 
well-stoppered  bottle.  A  little  should  be  decanted  off  for 
immediate  use  into  an  8-oz.  bottle  fitted  with  a  perforated  cork 
through  which  passes  a  pipette  with  i  or  2  c.c.  marks  on  it. 


/ 


341]      Analysis  of  Water  for  Drinking  Purposes     203 

Alkaline  Permanganate  Solution.  Boil  together  in  a  large 
basin  200  grams  of  caustic  potash,  8  grams  of  potassic  per- 
manganate, and  a  litre  of  water  until  the  solids  are  completely 
dissolved.  This  should  be  kept  in  a  well-stoppered  Winchester 
quart  bottle. 

Standard  Ammonium  Chloride  Solutions.  Two  solutions 
are  usually  prepared,  one  ten  times  as  strong  as  the  other. 
Dissolve  -117  (really  -11688)  gram  of  pure  crystallised  NH4CI 
in  a  little  water,  and  make  up  to  500  c.c.  with  ammonia- 
free  water.  Label  the  bottle  containing  this  '  Strong  NH4CI 
solution.'  One  c.c.  will  contain  -000074  gram  of  NH3,  or, 
when  the  ammonia  is  estimated  in  500  c.c.  of  water,  i  c.c. 
=  -01  grain  of  NH3  per  gallon.  For  the  '  weak  solution ' 
take  50  c.c.  of  this  strong  one,  and  dilute  to  500  c.c.  The 
NH4CI  should  be  tested  by  estimating  the  nitrogen  therein. 

Water  Free  from  Ammonia.  It  may  happen  that  the  ordi- 
nary distilled  water  supplied  in  the  laboratory  is  free  from  am- 
monia. This  may  be  tested  by  nearly  filling  a  testing  cylinder 
with  the  water,  adding  2  c.c.  of  Nessler's  solution,  and  stir- 
ring. If,  after  standing  for  five  minutes,  no  yellow  colouration 
appears  in  the  water,  it  is  sufficiently  pure  for  use.  Should  the 
slightest  pink,  brown,  or  yellow  appear,  the  water  must  be 
re-distilled  as  follows  : 

Place  as  much  of  the  water  as  can  conveniently  be  boiled 
in  a  large  flask.  Add  about  a  gram  of  recently  ignited  soda 
crystals.  Connect  with  a  condenser,  and  distil.  Test  20  c.c, 
of  the  distillate  from  time  to  time  for  ammonia.  As  soon  as 
no  further  ammonia  comes  over,  collect  the  water  in  a  clean 
Winchester  and  keep  it  very  carefully  stoppered.  In  this 
operation  it  is  very  necessary  to  use  soda  crystals^  as  the 
bicarbonate  always  contains  ammonia,  often  in  considerable 
quantities. 

341.    Free   Ammonia. — Place    50    c.c.    of  the   water 


204  Water  Analysis  [341 

under  examination  in  a  cylinder  of  clear  glass  standing  on  a 
white  tile,  and  add  2  c.c.  of  Nessler's  solution.  Allow  it  to  stand 
five  minutes.  Meanwhile,  place  in  another  similar  cylinder 
50  c.c.  of  ammonia-free  water.  Add  from  a  burette  'i  c.c.  of 
'dilute'  NH4CI  solution,  and  treat  with  Nessler  as  before. 
Should  the  colouration  in  the  two  cylinders  be  about  the  same, 
500  c.c.  of  water  must  be  used  for  the  determination.  Should 
it  be  darker  in  the  first  cylinder,  less  must  be  used. 

Fit  up  a  flask  and  Liebig's  condenser  of  the  form  ordinarily 
used  for  distilling.  The  condenser  is  usually  made  with  a 
glass  inner  tube.  In  many  laboratories  a  block  tin  tube  is 
preferred  on  account  of  the  superior  conductivity  of  the  metal, 
which  allows  of  a  much  shorter  condenser  being  used,  and 
thus  economises  space.  Pour  into  the  flask  about  250  c.c. 
of  ammonia-free  water,  and  add  a  gram  of  freshly  ignited  soda 
crystals.  Distil  for  a  few  minutes  to  wash  the  apparatus, 
testing  the  distillate  a  little  at  a  time  with  Nessler's  solution, 
until  it  is  quite  free  from  ammonia.  Now  pour  500  c.c.  of  the 
water  undergoing  analysis  into  the  flask,  and  distil,  collecting 
the  distillate  in  a  cylinder.  When  50  c.c  has  collected,  change 
the  cylinder  for  a  fresh  one,  and  estimate  the  ammonia  in  the 
50  c.c.  of  distillate  as  follows  :  Add  2  c.c.  of  Nessler's  solution, 
and  place  on  a  white  tile.  Now  make  a  comparison  cylinder 
by  running  '2  c.c.  of  'weak'  NHjCl  from  a  burette  into  50  c.c.  of 
ammonia- free  water  in  a  clean  cylinder.  Add  2  c.c.  of  Nessler, 
and  stir.  Place  the  two  cylinders  side  by  side,  and  compare. 
Should  the  comparison  cylinder  show  the  fainter  colour,  a  fresh 
one  must  be  made,  using  rather  more  NH4CI.  On  no  account 
must  a  further  amount  of  NH4CI  be  run  into  the  liquid  con- 
taining Nessler's  solution.  By  makmg  up  several  comparison 
cylinders  one  will  be  found  of  the  same  tint  as  the  distillate. 
The  amount  of  NH^Cl  solution  in  this  is  noted,  as  the  two 
cylinders  will  then  contain  equal  quantities  of  ammonia. 


342,343]  Analysis  of  Water  for  Drinking  Purposes  205 

By  the  time  this  test  is  finished  another  50  c.c.  will  have 
distilled  over.  The  ammonia  in  this  must  be  estimated  in  the 
same  way.  The  third  50  c.c.  will  probably  contain  no  ammonia. 
If  it  should,  it  must  be  estimated,  and  all  the  results  added 
together. 

342.  Albuminoid  Ammonia.— The  solution  of  'alkaline 
permanganate  '  whose  preparation  was  described  in  paragraph 
340  will  act  on  organic  matter,  liberating  the  nitrogen,  mostly 
in  the  form  of  ammonia.  This  ammonia  is  known  as  '  albuminoid 
ammonia.' 

To  the  liquid  left  in  the  flask  after  the  last  operation  add 
50  c.c.  of  the  alkaline  permanganate ;  distil,  and  estimate  the 
ammonia  in  each  50  c.c.  of  the  distillate,  exactly  as  in  para- 
graph 341,  until  it  ceases  passing  over.  When  the  water  is 
being  distilled  with  alkaline  permanganate  it  shows  a  great 
tendency  to  '  bump.'  This  can  be  lessened  by  putting  a  few 
pieces  of  clean  platinum  wire  in  the  flask. 

343-  Estimation  of  Oxygen  consumed  by  Organic 
Matter. — In  the  absence  of  nitrites,  sulphuretted  hydrogen,  or 
other  inorganic  reducing  agents,  a  very  good  idea  of  the 
amount  of  organic  matter  in  the  water  may  be  obtained  by  the 
action  of  a  standard  solution  of  potassium  permanganate  on  the 
acidified  water. 

Per?nanganate  Solution.  Weigh  out  accurately  '395  gram 
of  pure  permanganate  of  potash ;  dissolve  in  water,  and 
make  up  to  a  litre.  Each  c.c.  of  this  solution  will  contain 
•0001  gram  of  available  oxygen,  or,  as  is  very  frequently 
assumed  in  stating  results,  i  c.c.  of  the  solution  corresponds  to 
•0008  gram  of  organic  matter. 

Sodium  Thiosulphate  Solution.  Dissolve  10  grams  of  sodium 
thiosulphate  in  a  litre  of  water.  This  solution  alters  in 
strength  when  it  is  kept  for  some  time,  but  as  it  is  standardised 
whenever  it  is  used,  the  alteration  is  of  no  consequence.     For 


206  Water  Analysis  [344-346 

each  determination,  lo  c.c.  of  the  stock  solution  is  diluted  to 
loo  c.c. 

Sulphuric  Add.  Mix  50  c.c.  strong  H2SO4  with  150  c.c. 
water.  When  cool,  add  a  drop  or  two  of  the  standard  perman- 
ganate solution.  If,  on  standing  for  a  few  minutes,  the  acid 
does  not  remain  pink,  add  a  few  more  drops  until  the  acid  has 
a  faint  permanent  colour. 

344.  The  Estimation. — Carefully  clean  two  i6-oz.  flasks 
and  measure  into  one  of  them  250  c.c.  of  the  water  undergoing 
analysis.  Into  the  other  measure  250  c.c.  distilled  water.  In 
each  place  10  c.c.  permanganate  solution  and  10  c.c.  sulphuric 
acid  (prepared  as  in  paragraph  343).  Allow  them  to  stand  for 
four  hours  at  80°  F. 

After  this  time  add  to  each  a  few  drops  of  a  saturated  solu- 
tion of  potassium  iodide,  and  a  drop  of  starch  solution  ;  run  in 
the  dilute  sodium  thiosulphate  solution  from  a  burette  until  the 
blue  colour  entirely  disappears. 

345.  Calculation. — The  volume  of  permanganate  solution 
used  must  be  calculated  from  the  difference  between  the  volume 
of  thiosulphate  used  by  the  distilled  water,  and  that  used  by  the 

sample — i.e., =  volume  of  permanganate  used,  where  x 

is  the  number  of  c.c.  of  thiosulphate  used  by  the  distilled  water 
and  y  the  number  used  by  the  sample. 

The    weight    of    oxygen   for    70,000    parts    is    therefore 

X  —y        'ooi  X  70,000 
X  250 

(x  —y)o'2d>        .  11 

=  ^ rLi^— —  grams  per  gallon. 

X 

346.  Estimation  of  Hardnesfe. — The  hardness  of 
water  may  be  defined  as  its  soap-destroying  power,  and  is  due 
to  the  salts  of  calcium  and  magnesium  which  it  contains  in 


347]      Analysis  of  Water  for  Drinking  Purposes      207 

solution.  It  is  estimated  by  acting  on  a  measured  quantity  of 
water  with  a  standard  solution  of  soap.  Some  chemists,  how- 
ever, prefer  to  estimate  the  quantities  of  calcium  and  magnesium 
salts  by  a  more  scientific  method,  which  will  be  found  described 
in  paragraph  351. 

For  estimation  by  the  soap  method  (Clarke's  process)  the 
following  solutions  must  be  prepared  : 

Standard'  Calcic  Chloride  Solution.  Weigh  out  accurately 
I  gram  of  powdered  Iceland  spar ;  dissolve  this  in  dilute  HCl, 
taking  the  precautions  described  in  paragraph  10.  Evaporate 
to  dryness  on  the  water  bath ;  add  water,  and  evaporate  again 
until  no  HCl  remains.  Wash  into  a  litre  flask,  and  make  up 
to  the  looo-c.c  mark. 

Soap  Solution,  This  may  be  prepared  in  either  of  the  two 
following  ways  : 

{a)  Weigh  out  about  10  grams  of  Castile  soap  cut  up  into 
shavings,  dissoh^e  in  a  litre  of  35  per  c^nt.  alcohol,  and 
adjust  this  as  described  in  paragraph  347. 

{p)  Mix  in  a  mortar  150  grams  of  lead  plaster  and  40  grams 
of  dry  potassium  carbonate.  When  thoroughly  mixed,  treat 
with  50  c.c.  of  methylated  spirit.  Rub  well  round  the  mortar 
until  a  thick  cream  is  formed.  Dilute  to  about  400  c.c.  with 
alcohol,  and  allow  to  stand  in  a  tall  cylinder  so  that  the  lead 
carbonate  may  settle.  Filter  off,  and  adjust  the  liquid  to 
standard  strength. 

347.  Standardisation  of  Soap  Solution.— Pour  some 
of  the  soap  solution  prepared  as  above  into  one  burette,  and 
some  of  the  calcium  chloride  solution  into  another.  Measure 
out  into  a  6-oz.  stoppered  bottle  10  c.c.  of  calcic  chloride 
solution  and  60  c.c.  of  water  which  has  been  boiled  and  allowed 
to  cool  so  as  to  expel  all  carbonic  acid.  This  solution  will  be 
equivalent  to  a  water  having  10  grains  per  gallon  of  calcium 
carbonate    (10   parts   in    70,000).     Now    run   a  c.c.   of  soap 


2o8  Water  Analysis  [348,  349 

solution  into  the  bottle.  Replace  the  stopper,  and  shake 
vigorously.  A  lather  will  be  formed,  which  may  or  may  not 
disappear  on  standing.  Should  it  disappear,  add  another  c.c, 
and  repeat  the  operation  until  a  permanent  lather  is  formed. 
Note  the  quantity  of  soap  solution  required,  and  repeat  the 
operation,  running  in  o*i  c.c.  at  a  time  when  the  correct 
quantity  is  nearly  reached.  When  the  amount  has  been 
correctly  determined,  calculate  the  dilution  necessary  to  bring 
the  solution  to  such  a  strength  that  lo  c.c.  of  the  CaCl2  solution 
diluted  to  70  c.c.  with  water  requires  just  1 1  c.c.  of  soap  solu- 
tion. A  calculation  of  this  kind  has  been  described  in 
paragraph  62.  Dilute  to  the  extent  which  the  calculation  shall 
direct  with  alcohol  (35  per  cent.),  and  with  the  new  solution  so 
formed  repeat  the  experiment.  The  solution  will  not  give  quite 
the  result  expected,  and  will  probably  have  to  be  diluted  again 
after  making  a  fresh  calculation.  Repeat  this  alternate  titration 
and  dilution  until  11  c.c.  of  soap  just  gives  a  lather  with 
10  c.c.  of  calcic  chloride  and  60  c.c.  of  water. 

348.  Total  Hardness. — To  determine  the  total  hard- 
ness, measure  70  c.c.  of  the  water  under  examination  into  the 
stoppered  bottle  and  run  in  soap  solution,  as  described  in 
the  last  paragraph,  until  a  permanent  lather  is  formed  which 
will  not  subside  in  three  minutes.  Read  off  the  number  of  c.c. 
of  soap  required.  It  requires  i  c.c.  of  the  soap  to  produce  a 
permanent  lather  with  70  c.c.  of  water  ;  therefore  we  subtract 
I  c.c.  from  our  reading,  and  enter  our  result  as  degrees  of 
hardness.  Thus,  supposing  that  9*5  c.c.  had  been  used,  then 
we  should  say  the  total  hardness  of  the  water  was  8*5  degrees, 
or  that  I  gallon  of  it  contained  salts  of  calcium  and  mag- 
nesium equivalent  in  soap-destroying  power  to  8*5  grains  of 
calcic  carbonate. 

349.  Permanent  Hardness. — Measure  out  250  c.c.  of 
the  water,  and  boil  gently  for  half-an-hour.     Cool,  dilute  with 


350-353]  Analysis  of  Water  for  Drinking  Purposes  209 

boiled  distilled  water  until  the  volume  is  again  250  c.c,  measure 
out  70  c.c.  into  the  stoppered  bottle,  and  estimate  the  hardness 
as  before. 

350.  Temporary  Hardness  is  obtained  by  subtracting 
the  '  permanent '  from  the  total  hardness. 

HEHNER'S   METHOD   FOR   ESTIMATION   OF 
HARDNESS 

351.  By  this  process  the  carbonates  of  calcium  and  mag- 
nesium, which  have  an  alkaline  reaction  on  methyl  orange,  are 
estimated  by  titrating  with  decinormal  sulphuric  acid  in  the 
presence  of  that  indicator.  Since  the  temporary  hardness  is 
due  to  these  carbonates,  it  may  be  directly  calculated  from  the 
titration  of  350  c.c.  of  water. 

To  estimate  the  total  hardness,  add  to  350  c.c.  of  the 
water  50  c.c.  of  decinormal  sodium  carbonate  solution,  and 
boil  for  half-an-hour.  Filter,  dilute  to  the  original  bulk,  add 
a  drop  of  methyl  orange,  and  titrate  with  decinormal  sulphuric 
acid.  Thus  the  number  of  c.c.  of  sodium  carbonate  solution 
used  to  precipitate  the  sulphates  of  calcium  and  magnesium 
may  be  estimated.  Each  c.c.  corresponds  to  i  grain  CaC03 
per  gallon. 

352.  Nitrates. — The  nitrates  in  water  are  estimated  by 
dissolving  the  '  total  solid '  matter  (see  paragraph  339)  in  2  c.c. 
of  dilute  HCl,  and  placing  in  the  nitrometer,  together  with 
5  c.c.  strong  sulphuric  acid,  as  described  in  paragraph  114. 

REMARKS   ON   ANALYSIS   OF   DRINKING   WATER 

353.  From  the  results  of  each  of  the  determinations  which 
have  been  described  certain  deductions  may  be  made. 

Total  Solids.  For  drinking  purposes  the  quality  of  the 
solid  matters  is  of  far  more  importance  than  their  quantity.     But 

p 


2IO  Water  Analysis  [353 

for  certain  technical  purposes  this  determination  is  of  consider- 
able importance.  When  water  is  required  for  the  purpose  of 
raising  steam,  the  greater  the  quantity  of  solid  matter  the  greater 
the  quantity  of  '  boiler  scale '  that  will  be  produced.  Again, 
in  many  manufactures  where  soap  is  used  it  is  important  that 
the  water  be  as  free  as  possible  from  solid  matter.  On  the 
other  hand,  for  brewing  it  is  necessary  that  the  water  contain 
a  certain  quantity  of  sulphate  of  lime. 

Ammonium  Salts.  These  are  represented  by  the  free 
ammonia,  and  are  almost  always  of  animal  origin.  Seeing  that 
ammonia  is  one  of  the  first  products  of  the  decomposition  of 
animal  matter,  the  presence  of  large  quantities  of  ammonia  in 
water  points  to  the  fact  that  it  has  been  recently  contaminated 
with  sewage  in  some  form  or  other.  It  must  be  remembered, 
however,  that  the  ammonium  salts  are  not  in  themselves 
injurious,  and  that  their  presence  in  a  water  does  not  render  it 
unfit  for  drinking  purposes.  It  rather  puts  us  on  our  guard, 
and  directs  us  to  look  for  other  more  harmful  substances. 

Free  Ammonia  may  be  present  in  quantities  varying  from 
•0005  grain  per  gallon,  or  even  less  in  spring  waters,  to  2  grains 
per  gallon  in  shallow  well  waters.  Sewage  may  contain  8  grains 
per  gallon. 

As  a  rule,  water  should  contain  less  than  'oi  grain  per 
gallon. 

Albuminoid  Ammonia.  This  is  the  substance  which,  more 
than  all  others,  should  be  absent  from  drinking  water,  as  it  is 
generally  due  to  unchanged  sewage.  It  should  never  exceed 
•008  grain  per  gallon. 

Oxidisable  Matter.  This,  again,  is  an  indication  of  the 
organic  impurities  in  water,  not  necessarily,  however,  of  animal 
origin.  In  upland  surface  waters  the  oxygen  absorbed  should 
not  exceed  '3  grain  per  gallon.  In  other  waters  it  should  not 
exceed  '14  grain  per  gallon. 


353]       Remarks  on  Analysis  of  Drinking  Water      211 

Chlorides.  The  quantity  of  chlorine  in  water  is  of  very  little 
importance,  but  should  not  exceed  i  grain  per  gallon. 

Nitrates.  Like  ammonium  salts,  the  nitrates  in  drinking 
water  are  not  harmful  in  themselves,  but  their  determination  is 
useful  in  that  it  gives  us  an  idea  of  the  amount  of  sewage  con- 
tamination which  the  water  has,  at  some  time  or  other,  undergone. 
Nitrates  are  the  last  oxidation  products  of  sewage,  and  hence 
they  indicate  contamination  of  less  recent  date  than  that  indi- 
cated by  free  ammonia.  The  quantity  present  in  water  varies 
from  nothing  in  spring  or  shallow  well  waters  to  4  grains  per 
gallon  in  deep  wells. 

Hardness.  Here  all  the  remarks  will  apply  that  have  been 
made  concerning  total  solids,  except  that  the  hardness,  unless 
very  excessive,  cannot  be  considered  injurious  in  drinking 
waters. 


P2 


APPENDIX   I 

The  Atomic  Weights  (approximate)  as  used  in  this  Book 


Name 

Symbol 

Weight 

Aluminum 

Al 

27 

Barium 

Ba 

137 

Calcium 

Ca 

40 

Carbon 

C 

12 

Chlorine 

CI 

35-4 

Chromium 

Cr 

52 

Copper 

Cu 

63 

Fluorine 

F 

19 

Iron     . 

Fe 

56 

Magnesium 

Mg 

24 

Manganese 

Mn 

55 

Molybdenum 

Mo 

96 

Nitrogen 

N 

14 

Oxygen 

0 

16 

Phosphorus 

P 

31 

Platinum 

Pt 

194-5 

Potassium 

K 

39 

Silicon 

Si 

28 

Silver  . 

Ag 

108 

Sodium 

Na 

23 

Sulphur 

S 

32 

Zinc     . 

Zn 

65 

APPENDIX  II 

Factors  for  Calculation  of  Equivalents 


Amount  of 

Multiplied  by 

Gives  equivalent  amount  of 

NH3 

3-882 

(NH,),SO, 

NHg 

3-147 

NH.Cl 

NH3 

5 

NaNOg 

N 

1-214 

NH3 

N 

47 

(NH,),SO, 

N 

6-071 

NaNOs 

K^PtClg 

•193 

K,0 

K.O 

1-85 

K,SO, 

K^O 

1-585 

KCl 

KP 

2-146 

KNO3 

M&P,0. 

•64 

P.O5 

PA 

2-183 

Ca3(PO,), 

PaOs 

1-4 

CaP,0« 

PP5 

1-648 

CaH,(PO,), 

CaCOa 

-56 

CaO 

CaO 

1-845 

Ca3(P0,), 

CaO 

1-786 

CaCOg 

CaO 

2-43 

CaSO^ 

NaCl 

•53 

Na,0 

Mg,P,0, 

•36 

MgO 

INDEX 


ACE 

Acetic   acid,   estimation    in  silage, 

III 
Acidity,  estimation  in  silage,  no 
Adam's  process  for  fat  estimation  in 

milk,  i8i 
Adulteration  of  cheese,  198 

milk,  178 

Air  oven,  7 

Albuminoid  ammonia,  estimation  of, 

in  water,  205 
Albuminoids,  estimation  of,  in  grass, 

108 

r  in  oil  cakes,  93 

— roots,  n8 

Alcohol    method    for    estimation    of 

FegOs  and  AI2O3  in  mineral  phos- 
phates, 127 
Alkaline      permanganate      solution, 

preparation  of,  203 
Alkalis,  estimation  of,  in  soils,  171 
Alumina,    estimation    in   limestones, 

174 

mineral  phosphates,  127 

soils,  164 

Amides,  no 

Ammonia,  estimation  in  sulphate  of 
ammonia,  150 

Ammonia-free  water,  preparation  of, 
203 

Ammoniacal  nitrogen,  estimation  of, 
69 

Ammonium  chloride,  pure,  prepara- 
tion of,  171 

standard,  preparation  of,  203 

—  molybdate,  preparation  of,  131 

Apatite,  129 


Areometric  method  of  fat  estimation 

in  milk,  183 
Argands,  16 
Ash,  estimation  of,  in  butter,  190 

in  cheese,  198 

grass,  108 

oil  cakes,  92 

roots,  118 

Available  phosphoric  acid  in  soils,  159 
—  potash  in  soils,  159 


Babcock's  method  of  fat  estimation 

in  milk,  184 
Balance,  i 

—  adjustment  of,  3 

—  rough,  105 
Barley  meal,  104 

Basic  slag,  analysis  of,  130 
Bats'  guano,  138 

Bench  for  nitrogen  estimation,  57 
Bessemer  slag,  analysis  of,  130 
Bichromate  of  potash,  standard,  pre- 
paration of,  47 
Boiled  bones,  135 
Bone  ash,  135 

—  flour,  135 

—  meal,  analysis  of,  134 
Bones,  boiled,  135 

—  dissolved,  144 

—  raw,  135 
Bunsen  furnace,  60 
Burner,  Argand,  16 
Burning  filters,  17 
Butter,  analysis  of,  190 

—  remarks  on  analysis  of,  197 


2l6 


Index 


Cake,  manure,  analysis  of,  148 
Cakes,  oil,  analysis  of,  92 

remarks  on  analysis  of,  99 

Calcium  carbonate,  pure,  171 

—  chloride,  standard  solution,  207 

—  estimation  of,  28 

—  oxalate,  ignition  of,  29 

precipitation  of,  29 

Cambridge  coprolites,  129 
Canadian  apatite,  129 

Carbon  dioxide,  estimation  of,  31 

—  estimation  in  soil,  167 
Carbonates,  estimation  of,  31 

in  soil,  167 

Casein,  estimation  of,  198 
Castor  cake,  149 

Chalk,  solution  of,  9 
Cheese,  adulteration  of,  198 

—  analysis  of,  198 
Chlorides,  estimation  of,  44 

in  soil,  167 

Chlorine,  estimation  of,  44 
Chlorophyll,  iii 

Citric  acid,  action  on  soils,  158 

method  for  estimating  phos- 
phoric acid,  124 

Cochineal,  39 

Combined  water,  estimation  of,  in 
lime,  176 

in  mineral  phosphates,  121 

Combustion  method  for  nitrogen 
estimation,  58 

Comparison  of  methods  for  nitrogen 
estimation,  66 

Compound  manures,  analysis  of,  151 

Condition  of  oil  cakes,  100 

Coprolites,  129 

Cotton  cake,  100 

(manure),  148 

Creamometer,  T79 

Crude  fibre,  analysis  of,  108,  118 

estimation  of,  in  grass,  106 

in  roots,  113 

Curd  in  butter,  190 

Dairy  produce,  analysis  of,  178 
Decinormal  solutions,  38 


Decorticated  cotton  cake,  100 

Desiccator,  4 

Diastase,  preparation  of,  102 

Dissolved  bones,  analysis  of,  144 

Distillation  of  ammonia,  63 

Dolomite,  176 

Dry  matter,  analysis  in  grass,  107 

in  roots,  118 

Drying  apparatus,  5 

—  gases,  35 

—  precipitates,  15 

Dyer's  method  of  soil  analysis,  15^ 


Entry  in  note  book, 
Erdmann's  float,  41 
Evaporation,  8 
Extractor  for  oil,  93 


Factors,  26,  213 

Fat,  estimation  of,  in  milk,  181 

—  foreign,  in  butter,  191 
Feeding  materials,  analysis  of,  92 

—  meal,  analysis  of,  102 
Fehling's  solution,  preparation  of,  51 
Ferric  oxide,  estimation  of,  in  lime- 
stones, 174 

in     mineral     phosphates, 

126 

—  soils,  164 

Fibre,  crude,  analysis  of,  108,  118 

estimation  of,  in  grass,  106 

— in  roots,  113 

—  woody,    estimation   of,    in  cakes, 
97 

in  grass,  106 

Filling  U  tubes,  35 

Filter  pump,  14 

Filtration,  rules  for,  11 

Fineness,  estimation  of,  in  slag,  133 

Fish  manure,  analysis  of,  138 

Fletcher's  muffle  furnace,  16 

Foreign  fat  in  butter,  191 

Free  ammonia,  estimation  of,  in  water, 

203 
Furnace,  Bunsen's,  60 


Index 


217 


Furnace,  muffle,  16 

Fusion   method   for    analysis    of 

soluble  matter  in  soils,  169 
—  mixture,  preparation  of,  170 


Gas  lime,  analysis  of,  176 

Gas  regulator,  7 

Geissler's  pump,  14 

German  phosphate,  129 

Glaser's  method  for  estimating  oxide 

of    iron    and  alumina  in   mineral 

phosphates,  126 
Glucose,  estimation  of,  52 

—  —  —  in  roots,  116 
Gluten,  estimation  of,  103 
Grass,  analysis  of,  104 
Gravimetric  determinations,  19 
Guano,  analysis  of,  136 

—  Bats',  138 

—  meat,  138 

• —  Patagonian,  138 

—  Peruvian,  138 

Gunning-'s   method   of  nitrogen  esti- 
mation, 61 


Hardness,   estimation  of,  in  water, 

206 
Hay,  analysis  of,  104 
Hehner's   method  for  estimation   of 

hardness  in  water,  209 
Hydrochloric  acid,  estimation  of,  44 
Hydrofluoric  acid,  method  for  analysis 

of  insoluble  portion  of  soils,  169 


Ignition  of  precipitates,  16 
Indicators,  39 

Insoluble  albuminoids,  estimation  of, 
in  grass,  108 

—  alkalis,  estimation  of,  in  soil,  171 

—  ash,  estimation  of,  in  grass,  108 

—  phosphoric  acid,  estimation  of,  in 
superphosphate,  140 

—  portion  of  soil,  analysis  of,  168 
Iron,  estimation  of,  20 


mp:a 
Iron,  estimation  of,  in  hmestone,  174 

in  mineral  phosphates,  127 

soils,  104 

volumetric,  47 

—  tubes  for  nitrogen  estimation,  58 


Juice,  analysis  of,  in  roots,  114 


Kainit,  analysis  of,  149 

Kjeldahl's   method  for  estimation  of 

nitrogen,  61 
Koettstorfer  number,  192 

Lacmoid,  40 

Lactic  acid,  estimation  of,  in  silage, 

III 
Lactometer,  179 
Lime,  analysis  of,  176 
—  estimation  of,  28 

in  guano,  136 

•  limestone,  163 

mineral  phosphates,  128 

refuse  manures,  147 

slag,  130 

soil,  164 

superphosphate,  143 

Limestone,  analysis  of,  173 
Linseed  cake,  100 
Litmus,  39 
Lunge's  nitrometer,  80 


Magnesia,  estimation  of,  in  lime- 
stone, 175 

in  soils,  165 

—  mixture,  preparation  of,  27 

Magnesium  ammonium  phosphate, 
solubiHty  of,  125 

Maize  meal,  104 

Malt  dust,  104 

Maltose,  103 

Mangels,  analysis  of,  11 1 

Manure  cake,  analysis  of,  148 

Manures,  analysis  of,  120 

Meal,  analysis  of,  102 


2l8 


Index 


Measurement  of  nitric  oxide,  69 

Meat  guano,  138 

Methyl  orange,  40 

Microscopic  examination  of  oil  cakes, 

lOI 

water,  201 

Milk,  analysis  of,  178 

Mineral  phosphates,  analysis  of,  121 

Moisture,  estimation  of,  5-7 

in  bones,  134 

butter,  190 

cheese,  198 

grass,  104 

guano,  136 

hay,  104 

mineral  phosphates,  121 

oil  cakes,  92 

refuse  manures,  146 

roots,  112 

soils,  162 

superphosphates,  146 

Molybdate  and  magnesia  method  for 
estimation  of  phosphoric  acid,  132 

—  method   for  estimation    of  phos- 
phoric acid,  131 

Mountain  limestone,  176 
Mucilage  in  linseed  cake,  loi 
Muffle  furnace,  16 
Muriate  of  potash,  analysis  of,  149 

Nessler's    solution,   preparation  of 

202 
Nitrate  of  soda,  analysis  of,  151 
Nitrates,  estimation  of,  69 

— in  soils,  166 

water,  209 

Nitric  nitrogen,  estimation  of,  69 

—  oxide,  measurement  of,  74 
Nitrogen,  estimation  of,  56 

in  bones,  135 

dissolved  bones,  144 

grass,  108 

guano,  137 

nitrates,  69 

—  presence  of  nitrates,  66 

refuse  manures,  147 

soil,  i66 


Nitrogen,    estimation    of,    in   water, 

185 
—  organic,  68 
Nitrometer,  80 
Normal  solution,  definition  of,  37 

of  potash,  42 

sulphuric  acid,  40 

Note  book,  entry  in,  21 


Oil  cakes,  analysis  of,  92 

—  estimation  of,  in  fish  manure,  138 

in  oil  cakes,  93 

Organic  matter,    estimation    of,    in 
bones,  134 

in  mineral  phosphates,  121 

refuse  manures,  146 

soils,  161 

superphosphates,  139 


Palm  nut  meal,  104 

Patagonian  guano,  138 

Permanent   hardness,   estimation  of, 

in  water,  208 
Peruvian  guano,  138 
Phenol-phthalein,  40 
Phosphate,  German,  129 

—  mineral,  analysis  of,  120 

—  West  Indian,  129 
Phosphates,  estimation  of,  in  cheese, 

192 
Phosphoric    acid    available  in   soils, 

159 

estimation  of,  26 

citric  acid  method,  124 

in  bones,  135 

guano,  136 

mineral      phosphates, 

124 

oil  cakes,  148 

refuse  manure,  146 

slag,  131 

— soil,  162 

superphosphate,  140 

molybdate  and  magnesia 

method,  132 


Index 


219 


Phosphoric  acid,  estimation  of,  molyb- 
date  method,  131,  159 

soluble,  140 

Phosphorite,  129 
Platinum  cones,  15 

—  vessels,  16 

—  wire,  17 

Potash  available  in  soils,  159 

—  estimation  of,  24 

in  kainit,  149 

soil,  165 

—  manures,  analysis  of,  149 
Potassium  bichromate,  standard  solu- 
tion, 47 

—  permanganate,  standard  solution, 

50 

—  platinum  chloride,  weighing,  25 
Precipitation,  rules  for,  10 

Press  for  turnips,  113 
Purity  of  oil  cakes,  100 

Rabbits'  dung,  147 

Rape  cake,  149 

Raw  bones,  135 

Reduced  iron,  70 

Reducing  volume  of  gas,  table  for,  74 

Reduction  of  ferric  salts,  48 

Refuse  manures,  analysis  of,  145 

Reichert  number,  197 

Rice  meal,  104 

Richmond's  milk  scale,  180 

Rider,  3 

Roots,  analysis  of,  in 

Rough  balance,  105 

Salt,  estimation  of,  44 

in  butter,  191 

cheese,  198 

Samples,  82 

—  preparation  of,  90 
Sampling,  82 

—  grass,  87 

—  hay,  87 

—  limestone,  83 

—  liquids,  88 

—  machine,  83 

—  manures,  84 


Sampling  mineral  phosphates,  82 

—  oil  cakes,  87 

—  shovel,  83 

—  silage,  87 

—  soils,  88 

—  superphosphates,  84 

—  tool,  85 

—  water,  88 

Sand,  estimation  of,  in  bones,  134 

in  guano,  136 

manure  cakes,  148 

mineral  phosphates,  123 

oil  cakes,  93 

superphosphate,  142 

Schloesing's  method  of  nitrogen  esti- 
mation, 70 

Schroeder's  carbon  dioxide  apparatus, 
32 

Seminormal  solution,  definition  of,  37 

of  potash,  42 

sulphuric  acid,  40 

Sewage,  dried,  147 

Shoddy,  147 

Silage,  analysis  of,  no 

Silicates  in  limestone,  estimation  of, 

174 

—  in  soils,  estimation  of,  163 

Silver  nitrate,  standard  solution  of,  44 
Slag,  analysis  of,  103 
Soap  solution,  preparation  of,  207 
Soda,  estimation  of,  in  soils,  165 
Soda  lime  method  of  nitrogen  estima- 
tion, 58 
Soil,  action  of  citric  acid  on,  158 

—  analysis  of,  157 

Solid  matter,  estimation  of,  in  milk, 

180 

in  roots,  118 

water,  201 

Solubility  of  magnesium  ammonium 

phosphate,  125 
Soluble  albuminoids,  estimation  of,  in 

roots,  115 

—  ash,  estimation  of,  in  roots,  115 

—  phosphoric  acid,  estimation  of,  140 
Soot,  147 

Soxhlet's-fat  extractor,  93 


220 


Index 


SPA 

Spanish  phosphorite,  129 
Standard  solutions,  38 

of  ammonium  chloride,  203 

calcic  chloride,  207 

potash,  42 

potassium  bichromate,  47 

permanganate,  50 

silver  nitrate,  44 

sugar,  52 

sulphuric  acid,  40 

Standardising,  41 
Starch,  estimation  of,  102 

—  in  linseed  cakes,  loi 
Steam  oven,  6 

Sugar,  estimation  of,  50 
in  roots,  116 

—  gravimetric  estimation  of,  54 

—  scum,  147 

Sulphate  of  ammonia,  analysis  of,  150 

potash,  analysis  of,  149 

Sulphates,  estimation  of,  23 

in  gas  lime,  177 

soils,  162 

Sulphur,  estimation  of,  in  gas  lime, 

177 
Sulphuric  acid,  estimation  of,  23 
method  of  nitrogen  estimation, 

61 

seminormal,  40 

Suspended  matter  in  water,  201 
Swede  analysis,  iii 

Table  for  areometric  method  of  fat 
estimation,  186 

limestone  analysis,  173 

manure  cake  analysis,  148 

mineral  phosphate  analysis,  120 

reducing  volumes  of  gas,  74 

refuse  manure  analysis,  145 

—  —  soil  analysis,  163 

superphosphate  analysis,  145 

Taste  of  cakes,  loi 
Temporary  hardness,  estimation  of, 
in  water,  209 


Transit  of  samples,  89 
Turnip  analysis,  in 

U  TUBE,  filling,  35 

Ulsch's    method    for    estimation    of 

nitrates,  69 
Undecorticated  cotton  cake,  100 
Units  of  valuation,  152 

Valuation  by  units,  152 

—  of  manures,  152 

mineral  phosphates,  155 

Voelcker  on  sampling,  84 
Volumetric  estimation  of  chlorides,  ^4 

iron,  47 

sugar,  50 

—  estimations,  37 

Wash  bottle,  13 

for  ammonia,  14 

Washing,  rules  for,  11 
Water  analysis,  200 

—  bath,  8 

—  combined,  5,  121 

—  free  from  ammonia,  preparation  of, 
203 

—  of  crystallisation,  5 

Weighing  potassium  platinum  chlo- 
ride, 25 

—  rules  for,  3 
Weights,  I 

Werner  Schmidt  method  for  fat  in 
milk,  182 

West  Indian  phosphate,  129 

Wheat  sharps,  104 

Will  and  Varrentrap  method  of  nitro- 
gen estimation,  58 

■  —  tube,  51 

Woody  fibre,  estimation  of,  in  grass, 
106 

in  oil  cakes,  97 

Zinc-dust,  67 


Spottiswoode  &*  Co.  Ltd.,  Printers,  New-street  Square,  London. 


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'J^t-  12  19.^'; 


FEB  241937 


MAn  10  1937<^' 


~7K 


^ 


J" 


^ 


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SEP  131^ 


LD  21-100m-8,'84 


(.?i- 


>Aa^ 


ye  51389 


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